Ooh, I’ve been waiting for this day…I hope we get some good discussions. I hope people don’t just look at it and say “Oop, it’ll never happen, 0%” without some hard evidence that it is impossible… After all, remember when the Japanese version of the 3DS came out last year? How many people saw Mewtwo’s trophy and considered him deconfirmed forever? This rule of ‘Assist Trophies can never be made playable. Ever.’ seems to have the same amount of backing as ‘They’re a trophy, so they’ll never be playable. Ever.’, and we all know how that one turned out.
Chance: 85%
Personally, I would give this a high chance of happening. Maybe this is a bit optimistic, but this is asking if at least one of a vast number of characters ends up making it, so altogether it seems reasonable. After all, NOWHERE does it say that a single character can have only one role in the game, and can never ever change. Zelda/Shiek are both playable, yet the same person, as are Samus/Zero Suit and Mario/Doc. We can even talk about how Palutena is playable despite being in statues all over her stage, or that Toon Link can alternate between playable and Spirit Tracks conductor. And it’s not just limited to playable characters – Inky, Blinky, Pinky, and Clyde are all stage hazards on Pac-Maze, but that doesn’t prevent them from being Assist trophies as well (or elements of PAC-MAN's moveset...). Assuming any character was promoted, the developers could easily take the original form out of the game in some way. Or not, really – Smash has a history of letting the same character be on stage at the same time.
Really, I think one of the most important factors is that these characters were all popular enough to make it into smash, just not selected for playable. Would Nintendo rather bring in a new character with an unknown fanbase, or make an assist character playable who has a known fanbase? Particularly for some of the NPCs, Nintendo has even acknowledged their fanbases. I think it’s much more likely that Nintendo would rather make a NPC playable that they know will sell, over something like a third party from a series that is unknown in a decent portion of the world.
I’m going to split this up and discuss the chances of making the NPCs playable, in the order of ease:
- Current Assist Trophies/Pokéball Pokémon (Waluigi, Midna, Takamaru, Gardevoir, Zoroark, etc.)
There are currently 39 Assist Trophies and 41 Pokémon as NPCs. They appear to be selected based on a random number generator (RNG), which is very easy to replace or modify to not pick a certain number. In the case any of them is made playable, a single line of code could just reroll the RNG to get a different number and put up a different character. As a bonus, these characters are all modeled and rigged; some even have animations. Since animations and rigging are the hardest parts, this means that a lot of the work is done for the devs already. Some, like Waluigi, have several animations already, e.g. running, down attack, side smash, etc., making a very easy job for the dev team to just add in the remaining animations and take them out of the lists. Furthermore, the now vacant AT slot could be given to another character – if Midna were made playable and we needed another Zelda assist trophy, the devs could patch Impa or someone in to take her place while Midna sits on the select screen. Sakurai has even admitted some, like Takamaru, were considered for playability…and Little Mac has shown that the jump can be made.
- Current Stage Hazards/Bosses (Twinrova, Flying Men, Reshiram/Zekrom, Dark Emperor, Yellow Devil, Nabbit, 5-Volt, Metal Face, and some big purple dragon-looking thing)
These are really all over the place. Some, like 5-Volt, are too tied into the stage to be anything but a hazard; others, like the Bosses, are generally disliked on principle and people would rather they be out. One of the most common requests is a hazard switch – to be able to play the stage with platforms, but without a boss coming by to wreck everyone’s day. For the stages that have made it to 8-player mode, the hazards are all off, so we know there is a switch. The game could easily be set similarly to how Alfonzo takes over for Toon Link (“Leave it to me!”): If Ridley is playing on Pyrosphere, do not have Boss Ridley show up. Otherwise, fair game (or unfair, depending on how you see bosses…). Furthermore, as with the previous category, some of these have a lot of model rigging finished – Nabbit walks around and has a grab, Twinrova have movement and a special attack, while Ridley has almost a complete attack moveset. As before, some of these could be promoted to playable without breaking the stage, or at least having the stage’s hazard be deactivated if the character is playable (or at will – like I said, a lot of people want that too). And the stage icon can just be patched to a different one in case the character is displayed too prominently.
- Current Smash Run Enemies (Bonkers, Darknut, Shy Guy, Waddle Dee, etc.)
The 3DS version contains about 79 enemies in Smash Run, however only a fraction of this number appear in one round. As with the assist trophies, they can easily be commented out of the lists and made playable, and have several attack animations – most even have animations for lying prone and being grabbed. However, these are very generic enemies, so have little chance. What could happen, though, is that one is used as a base for a similar playable character, e.g. Bandana Dee could be made by using the animations that the Waddle Dee has in the game, again, making life easier for the devs.
- Current Stage Background Characters (Viridi, Tails, Silver, Knuckles, and a host of various Pokémon and Animal Crossing citizens)
These may be a bit tougher to include depending on what the stage is. With the exception of a few, the Animal Crossing citizens are all interchangeable and put in with a RNG– this means an individual could be commented out to appear as a playable character or another role (in case anyone wanted Mr. Resetti’s ‘assist’ trophy back). The Sonic characters, likewise, are sent at random times, and could thus be excluded from running across the stage – all of them also have rigging and a few animations. Viridi is a special case – she shows up to call the Reset Bomb down, but is only put up as a sprite. Thus, she could be replaced by a blank image, and then she never shows up on that stage, allowing her to be playable. The only ones who may be problematic are the Pokémon on those stages – they are not randomly put in, and are always the same. If any of them (e.g. Blaziken) were to be replaced, it may involve remodeling something a lot more complicated rather than just commenting out a RNG outcome.
- Current Playable Characters’ Moves (Toad, Chrom, Doc Louis)
These may not be able to make the jump. Despite having animations already, changing these would involve giving Peach a new sideB/Robin a new Final Smash/Little Mac new win poses.
So, in conclusion, I don’t think that a character existing in Smash already permanently cements him to one spot, particularly if he has a big enough fanbase. Anything can happen, and a lot of the highly requested characters are in the game, but not in the way we’d have liked. And there’s no rule that says things can’t change…
TL/DR: There’s no rule saying they can’t, and most of the NPCs are very popular characters. Most can easily be taken out of their current role and make playable.
Want: 100%
I’d go higher if I could. Aside from K.Rool, everyone I want playable is either a veteran or an NPC. And really, it would not bother me at all if Midna or Ghirahim called him/herself as an assist while playing, or if Boss Ridley showed up to wreck Playable Ridley’s day, or whatever. I would just like to see these popular characters playable, and I think they have a better chance than obscure third-parties or niche first-party characters.