I dont believe the leak per se, but i do think it has some merit over other leaks, not credibility but merit worth discussing.
first off i'll just say the mysterious nature of a riddle for a leak gets people talking and the fact it was taken down a few times adds some initial notoriety, so thats partly why its still being discussed, it simply got on everyones mind.
but its an odd leak to fake as it has snake returning after the bad blood between konami and kojima, sora from kingdom hearts so it connects to disney and then characters like goroh, medusa, and porky who very few people are guessing at. so this would seem like a leak that should get discarded immediately however upon further analysis these are all characters that COULD actually make sense to choose if you follow a certain train of thought:
wolf and ice climbers everyones guessing at so no debate there for or against this leak.
simon is an odd choice because of the whole kojima and konami thing with snake so sakurai even going to them for anyone would be strange BUT we have the one leak from a somewhat credible leaker, vergeben, saying simon is in and THEN later saying snake, where as the imgr leak had both from the get go. so yes imgr could have been "piggybacking" onto the one somewhat credible leak but the imgr leak went out on a limb with adding snake and now vergeben agrees. snake coming back makes sense if you assume snake was heavily requested on the ballot so sakurai went to konami to get him back and then got simon as well despite the kojima fued.
ridley gets chosen this time due to the ballot so sakurai decides to bring back another "boss" from brawl, porky, which could also be due to earthbound on the SNES classic OR even the fact that sakurai has a history of shaking up the industry with smash characters. fire emblem basically came to the west after he added it to melee and kid icarus was revived after he added pit to brawl, this could be his attempt to make mother 3 relevant again and bring it to the west finally as fans have been begging for it for years. obviously not the only reason to choose porky but it could be part of it and would be a very sakurai move, and again porky is a character with a history in smash as a boss. If sakurai was racking his brain to come up with how to get ridley to work to please fans he may have also been thinking about how other bosses could work from brawl and this time hes got it and so we are getting porky too.
goroh was the first assist trophy revealed, and f-zero is also a game on the super nes classic so theres some relevancy here. earthbound and fzero have also both been a part of smash since the original 64 so its not that crazy to finally give them some more characters even if very few people are guessing they would get anyone. if those "lesser" known series that have been in smash since the begining got anyone, goroh and porky would be those choices as they are already smash relevant included in the series in some form in the past, theres a precedence for them here and again few are guessing at them despite that. Goroh was also in the opening to melee so if we get ridley/goroh/wolf we have ALL the characters that people thought might be in melee because they were in that opening cinematic, they have a precedence in smash for a long time so despite few guessing at them they have been rubbing shoulders with our smash crew for a while.
medusa is from kid icarus and sakurai obviously has a slight bias or at the very least can do as he pleases with characters from that series so if hes looking for "villians" for some unknown "mode" or theme this game might be going for she fits. past games never had a theme but sakurai does something new EVERY smash and when you guess at what happened last time you are always blind sided by sakurai mixing up his game. Also kid icarus is on the nes classic so again relevancy here with how well those systems sold, medusa has been the kid icarus enemy from the start.
the imgr leak guesses geno AND mallow and nintendo tweeted about BOTH of them in a "which team are you on" question. nintendo NEVER mentions mario rpg let alone those two square/nintendo joint ownership characters and to mention both when nearly everyone who would guess at geno or fake a leak with him would NOT tack on mallow but this leak did and nintendo mentioned BOTH characters recently. also mario RPG is another game on the SNES classic, so once again somewhat relevant. Geno also had music cut in brawl, got a newcomer splash art when his costume was shown off in smash 4 DLC ect... obviously im bias here but the dude has a lot going for him.
chorus kids is an odd choice but we know it was part of the gematsu leak back in the day so almost certainly a character that was planned and scrapped for smash4, probably due to the 3ds limitations, and its highly likely we could see them in this iteration, not surprising to leak them at all so doesnt really tip the scale for or against the leaks credibility.
K Rool and DIxie are both highly requested and with Wolf/K Rool/and Ridley almost all certainly being high on the smash ballot the idea of doing heros vs villians this time might be sakurais way of acknowledging that fans seem interested in that "flavored" theme with all the villians they heavily requested.
takamaru is being guessed by lot so of people as our retro rep, his games more relevant due to being released in the west, he got a mii cotume so he fits with k rool and inkling in that regard and he was an assist trophy so he fits with little mac and goroh there as well, hes a pretty safe guess so nothing to weigh in on the leaks credibility here but he makes sense.
mimikyu and elma are our "newer" reps but they both make a lot more sense than some reps most people guess at for more current stuff like rex/pyra or an ARMS rep or something as they "fit" the time frame better for when sakurai would finalize the roster. their games would be relevant at that time so they would be characters sakurai would choose at that initial stage. xenoblade 2 and ARMS or some future pokemon all might not have been on sakurais radar at all, and even decidueye seems more popular after sun and moons fans had time with it while gamefreaks pushed mimikyu harder as part of the marketing so would have probably requested he get in smash to sakurai over others who might have become "fan favorites" but at a slightly later date.
now finally sora whos such a terrible choice for a "fake leak" as that means disney square and nintendo all have to get along and just seems like it would be a mess BUT surprisingly a bunch of stuff has recently come up in favor of sora. specifically the odd series of events surounding the smash player zero. he who won the smash invitational last time (so that makes him kind of the "official" leader of professional smash players in the eyes of nintendo and stuff), he out of the blue starts streaming kingdom hearts and almost immediately after hes done laying through the games he gets invited to an early KH3 event...why?? why did a smash player out of the blue stream KH and then much starnger still immediately get to go look at KH3 early?? and then even though zero is retired and says he didnt want to do anything with smash 5...he gets invited to E3 again a few weeks after the KH event and says yes to going. i mean of course he would be invited and yes this isnt the typical thing to say no to just to stay "retired" but theres a "link" there with the KH stuff thats at the very least interesting... Then the youtuber HMK posts a video talking about the chances of sora in smash and his conversation with a disney executive actually seems to dismiss the "impossibility" of negotiating with disney, seems if it came up theyd say yes (
https://youtu.be/CV76QegRezE ) so suddenly sora, a character who you'd be foolish to add to a fake leak and expect anyone to take you seriously has some actual evidence backing him right as we lead up to E3. If square is still involved with smash (and i think they will be) they might very well want to push sora in smash as KH3 is approaching release and im sure the smash ballot has KH pretty heavily requested despite its perceived implausibility due to the negotiations with disney.
theres also a lack of mario/zelda characters in this leak which is again not what youd expect to "fake", EVERYONE guesses captain toad and hes not here. but this could also make sense as geno might be the "mario" rep (at least in the base roster) and a lack of a zelda rep could be explained with the BOTW link we saw. if link or zelda and maybe even ganon got overhauled it would feel like the series got attention without a newcomer so to not include a zelda rep actually isnt that crazy even in favor of instead getting earthbound and fzero reps, cause it would still feel like all the series got somewhat equal attention if several zelda characters got reworked. mario having cappy added to him somehow could also explain the lack of mario reps while the series still gets attention and so maybe save the newcomers for DLC as captain toad will sell better than say medusa, so you put your time into her on the base roster and save the mario newcomer for the DLC. some of the oddities of this leak make sense when you really pull it apart.
So there ya go my lengthy analysis of the imgr leaks credibility. no it doesnt have a ton of credibility but it has a lot of odd choices, a few things like guessing snake before vergeben while also "piggybacking" on what he leaked first. while that isnt that hard to assume (simons in so theres a good chance to guess at snake too) its at least remained consistent there. these odd choices also line up the more you think about them and it would take a crazy amount of thought to post a seemingly strange roster that instead of crumbling under scrutiny actually becomes more acceptable, this is often how final smash rosters feel, stuff you wouldnt guess at really (wii fit trainer) but when you look at it from a certain perspective or train of thought it makes sense. Its mostly just something to discuss before E3 but i see a lot of people saying thats the only reason we are discussing it but theres a bit more too it then that, plenty of random leaks on the internet to discuss this one at least has a few special things about it that make it a little more practical to keep in mind and take semi-seriously for now.