What was said right here isn't unreasonable at all. Think about; Mario is Nintendo's biggest and most important franchise and thus had the most characters in Melee with 5 reps (Mario, Dr. Mario, Peach, Bowser, and Luigi.) Dr. Mario is pretty much guarenteed gone because the other two "super clones" (Roy and Pichu, as I call them) have been shot down by other updates (Ike now has Roy's ALTS and Pikachu has Pichu's, for example) and the second trailer showed that many of Dr. Mario's attack effects (directional influence, power, etc) have been intregrated into Mario's. This leaves a spot to fill and the main people in running are Bowser Jr (despite being knocked down by multiple factors brought up by several updates), Geno, and Paper Mario. When this spot is filled it gives the Mario franchise 5 characters once again.
Now, remember how I said that the Mario franchise is basically sets the high bar? Currently, the Mario franchise has 3 reps with Mario, Peach, and Bowser and Luigi is obviously going to return so that gives it 4. Every nonunlockable franchise (except Yoshi, of course) that has only had one rep from the get-go since the original has been given at least one new rep: Pokemon: Pokemon Trainer, Kirby: Metaknight and King Dedede, Metroid: Zero Suit Samus, DK: Diddy Kong and if the holes theory is correct, Star Fox: Krystal. Because of this, the bar has naturally been raised and to point this out even more, because of the Pokemon Trainer, Pokemon already technically has 4 reps. Now, unless both Jigglypuff and Metwo are given the boot, Pokemon's fighter count will probably be six because it'd be foolish to say that the franchise won't have at least one unlockable newcomer *coughlucariocough*. Even if this does turn out to be the case, the pokemon franchise would end up with a minimum of 5 reps.
Because of the high bar I mentioned, the Mario franchise would have to go over (or meet) this amount. 5+1=6, ZOMG, astounding! This would line up with the equilibrium that Melee established: Mario: 5 reps, Pokemon: 4 reps, Zelda: 4 reps. This would also make sense because, both in sales and in number of games, this lines up perfectly (at least for Mario and Pokemon because Kirby has the third most games of any Nintendo franchise but is behind Zelda in sales). So, in the end, you'd have one person replacing Dr. Mario and one newcomer added with no strings attached and all is well in the world.