I have not commented in the Isaac thread this round. However, there has been a large Isaac movement for pre-Brawl, pre-Smash 4, and now pre-Ultimate. He is the only character left that has had a very large fanbase for the last ten years.
If I may offer some hope. I was a major supporter of Ridley for the last 17 years (if not the preminent supporter of Ridley), and I heavily pushed for Roy's return in Smash Bros. as well. It got REALLY hopeless for both of these characters after Smash 4. Sakurai went on the record to say Ridley was indeed too big and resizing him would "not make him faithful to who Ridley really is" and Roy had to contend with the fact that there was already four Fire Emblem characters in the game (one of which was a Marth clone) and the fact that since so many Brawl veterans got cut, many viewed his return as low priority at that point. Flash forward to nine months later, Roy despite all odds, returns as DLC for Smash 4.
Ridley, a character with the distinction of being turned down three times and then having Sakurai personally pour cold water on the character, managed to somehow be greenlit only a year after Sakurai made his statements regarding Ridley (Sakurai made his statements on Ridley in November 2014 while the first project plan was submitted in December 2015). Ridley made it in despite all odds. I honestly was never expecting him to be added in after Smash 4.
Look at Young Link and Pichu too? I bet their supporters thought that they would never be in another Smash Bros. game, yet here they are now.
K. Rool needed the ballot to make it in. He was a character who had not been in his own series since 2007, and had not made an appearance outside Smash Bros. since 2008. Many thought he was a shoe-in for Smash 4 or its DLC.
Chrom and Dark Samus are also good examples. Chrom was yet another example of a character whom Sakurai poured cold water on (he said the character was too similar to Marth and Ike), and he was kind of a butt monkey in Smash 4 (see the Robin unveil trailer and the Palutena's guidance for Robin). There was also the general fatigue in general for Fire Emblem to the point where it had become the one series where groans can be heard if the topic of newcomers for it comes up. There was also the fact the character was quickly becoming old news in his own series, with Fates, Shadows of Valentia, and now Three Houses being all more current games to the series. Chrom still made it in due to fan demand.
Dark Samus might have the single most incredible story of making it into Smash Bros. of them all. Ridley, a character that had been heavily requested for over 17 years only made it in with this game. Dark Samus's peak popularity was with the pre-Brawl era. Like K. Rool, her last appearance in her own series was all the way back in 2007, and unlike K. Rool, its unlikely she will ever actually be a part of the storyline again. Metroid Prime content in general always left much to be desired, and in Smash 4 in particular the only Prime trilogy content outside a few songs (all either rips or ports from Brawl) was the Assist Trophy of Dark Samus (all the other Metroid content was mostly stuff from Other M, and a few things from Super/Zero Mission). Most of her dedicated fanbase evaporated as Metroid fans tried to circle the wagons to try to get Ridley in. Ironically it might have been due to Sakurai's own statements on Ridley as to why Dark Samus might have done as well on the ballot as she did (Metroid fans might have been broken on Ridley ever happening and voted for Dark Samus instead so that some sort of Metroid villain got in). Despite all odds, Dark Samus made it in.
I am not saying Isaac is going to be in. Heck, there is a good chance Isaac might not even be an Assist Trophy. However, with the Ultimate a lot of the impossible has been made possible. A lot of the conventional wisdom has been shattered. Who would have thought Daisy would make it in as our Mario newcomer over the likes of Toad, Geno, Waluigi, Paper Mario, and Captain Toad?
Just keep expectations low, and you might be surprised. Sakurai's own words in the last dedicated Smash Bros. direct was that there were only a few more fighters left to be unveiled. He has already unveiled K. Rool and Isabelle after this statement. Realistically, there likely is not any more than five fighters left at this point, with there possibly being as little as only three more (one more non-echo and two more echoes).
If Isaac for whatever reason does not make it in as an Assist Trophy or fighter, its not necessarily the end. He could potentially be DLC. Just support the character. However, those who think he is "likely" are setting themselves up for a disappointment. Just support him. Realize the journey is likely going to get you kicked in the face quite a bit along the way. Ridley fans had this extensively. K. Rool fans too. If Isaac is their equal, it is his turn to eat pain.
Now, if those rumors of a Golden Sun remake on 3DS are true. I would absolutely implore Golden Sun fans to purchase the hell out of that game. Do not cry or whine that is on an outdated console or that you hate handhelds. If you truly care about the future of Isaac. The future of Golden Sun and its universe. You would not only buy that game, but you would try your best to get others to play it too. That is absolutely your last chance to save the franchise. Going about thinking you can save the franchise just from memeing Isaac into Smash Bros. is backwards. If Golden Sun's remake does well it puts him in a much better position going forward. Do not. Do not. Do not. Do not. Do not. Do not. Do not. Pirate the game. $40 to support your character and franchise of choice is not a hardship. It is your duty. Words talk. Actions walk.
I myself am sympathetic to Isaac and Golden Sun fans even though I am still not even through the first game in the series (I bought both of the GBA games during the last four years). I hope some day I can appreciate this series like the rest of you. However, you will need to realize that in this journey, the paths and obstacles will not be the same as what others have faced. Everyone has their own journey. Appreciate the strength of others while you cultivate your own. This journey might be over in a few months, or it might take another decade. Keep at it.
There are very few important and iconic Nintendo characters left not yet playable yet in Smash Bros. Dixie Kong, Toad, and maybe Bandanna Dee might be all that is left. Isaac is on the knife edge between being an "all-star" and just a "cult favorite". After Brawl's release, the fanbases of many characters that failed to make it in after Brawl collapsed after a few years. Of the few that did not, they were Ridley, K. Rool, Mega Man, Little Mac, Bowser Jr., and of course Isaac. All of these characters except one is now in.
Isaac stands alone in history AND prestige. Isaac is not Ridley. Isaac is not K. Rool. Isaac is not Roy. Isaac is not Dark Samus. Isaac is not Chrom. He is facing his own unique circumstances against him and his journey is different. However, where all the journey lie as one is the adversity. The downs. The lows. And the blows. You can know things look bleak, but still press forward. Still fight on to the tomorrow. Know that your next destination might not bring you to where you hoped to be. But still press on. Press on. Chanel the dream within and extend it through hope and heart.
If Golden Sun is brought back through a remake, that is where you must absolutely fight. That is your opening. Fight. Fight. Fight. Fight. Fight. And Give no Respite. You have to buy the game. The game from which my avatar hails (Fire Emblem Thracia 776) was released when the SNES was nine years old, and yet it still ended up being a masterpiece and still to this day one of the best games in the series in my opinion. Kirby's Adventure was released when the Famicom was 10 years old and is widely regarded as one of the platform's foremost masterpieces. A remake/retelling of the series for the 3DS would absolutely be the series's last chance. TAKE IT. RUN WITH IT. FAST. FASTER. EVEN FASTER.
As I told hopeless Roy fans four years ago. Onward. Together we ride.
Isaac for Smash Bros.
May the Sun Shine On