I cannot honestly see a "heap of characters" at all. They take the most amount of time than anything else besides any Mode that requires a lot more data than any character(which is probably unlikely. While a stage(Orbital Gate) did take the same amount of time, it did clearly have more programming than other stages and as we know, was not the only thing being worked on). There's just way too many variables to make them super easily. Nearly 30 different moves(that includes customs), more costumes than originally, and unlike in previous games, heavy emphasis on game balance. They're going to take a very long time to get right overall. And there is no guarantee Paid DLC will be severely popular for Smash. Not enough to just suddenly throw out characters. They may do a few more(likely veterans people were annoyed that were cut, less so Pokemon because the series was very well done, so they don't feel jipped with the content, and moreso StarFox and Mother, which got more content removed and almost nothing to make up for it. Pokemon cannot actually say that, as it was repped severely well overall beyond, you know, stages, which also would not be that hard to remake. I can see more stages from various series. Poke Floats, regardless of some silly music rule, as nobody said it couldn't repeat the music at all, is pretty darn easy for them to remake. It's just objects floating around in a set pattern. No A.I. to deal with, after all. Or Pokemon Stadium 1, ported from Brawl. I honestly do think Wolf and Lucas have a better chance right now, mostly Wolf, as it'll gauge players' interest(which no, we cannot literally know how the majority will feel until it properly happens) a lot better than Mewtwo. He's a less super popular character and would actually make sure people don't mind Paid DLC for Smash characters, even if they aren't the ultimate most popular ever).
I agree Mewtwo is not a great way to test it, but it's more because the deal sullies the facts a bit much. We don't even know the price for him just yet. Although him already being severely popular(and not because he's a Pokemon, but because he's the most heartfelt cut of Smash overall) means that it severely appeals to Smash fans, but not much else. On the other hand, Paid DLC is pretty much designed for more dedicated fans, which aren't usually casual fans(there's an irony here). One thing to note is that an average Smash player is intended, by Sakurai, to be the casual fanbase. They buy the game, and play it. Paid DLC is not really meant to directly appeal to them, but to the more hardcore/competitive crowd. Same with Patches in general. Balance Patches are pretty clearly more appealing for competitive players, even if they benefit everyone well. Having a more balanced game is great for tourneys. The actual idea is that the casual fanbase aren't about tourneys. It doesn't mean they don't like balance, but they aren't viewed as caring more about it. It's quite clear that this game appeals more to the competitive crowd, even if it has nothing to do with Omega Mode(that was made because people wouldn't try out other stages online, which had so much lag that it wasn't ever viable for competitive play. It's pretty much a casual way to play. Even going so far as forcing items heavily, with no real balance to it). All For Glory literally did was just add another interesting option. FD just isn't that balanced, which Battlefield does better, so it seriously isn't a competitive setting based upon the stage, just the fact it's 1 on 1 without items instead.