sorry i didn't explain my theory well:
popo and nana i've HEARD have seperate cards so do samus and zerosuit samus and pokemon trainer is split into 3 cards then you add shiek to one of the unknowns and you'd get 25 starting characters.
i think 25 starters is likely because that is the total number of melee characters. so if you take all the known characters subtract snake and sonic you have 20 starters known, and according to the 30 cards covering all the starters theory we have 6 spots left(since ice climbers, pokemon trainer, and samus are split into multiple cards). if shiek is one of those spots we get 5 spots left that probably contain ganondorf (leaked) and the obvious captain falcon.
the final 3 spots could be any combination of highly likely veteran starters such as marth, mewtwo, ness, or mr. game and watch. or some highly likely "starter" newcomers krystal, ridley, animal crosser. or most likely some unknown combination of a few veterans and a few newcomers.
it is possible that pokemon trainer is 4 cards or that these 30 cards also cover sonic and snake and then this 25 starting character theory is dead. tho if they did cover sonic and snake i'd assume they have NOTHING to do with the starting roster anyway...