The whole recent thing doesn't quite apply to characters as it does to stages, and yes, there are stages that are indeed retro, but the vast majority aren't. There will by outliers, but they are just outliers. Thuuus, we could get a Other M stage and a Fusion stage, instead of Prime 3. We could get a Prime 3 stage and then a Metroid II stage. Not bloody likely, but it can happen.
For the most part, and I stress the qualifier of "most part", stages go into three groups: Based off of the most recent parts of series, based off of oldest part of series, and general representation of the series. on elements from each game. What qualifies for "series" may be a bit hazy, since I would say that you could separate Prime from the regular Metroid canon, just as easily as you would separate any of the Mario spin offs from the platformers. Also, I'd say that if the most recent iteration is already covered, then the next most recent may be taken as well (Pirate Ship) Of course, there are certain stages that don't hold true to these theoretical rules at all, such as Halberd, or Temple, but those are very few.
Also, while its clear that there was no requirement for stages to be based on games that came out between Melee and Brawl, I think there may have been a general theme for that. Nothing set in stone though.
Edit: Oh yeah, we need to see Little Birdie in Smash 4 in some form.....maybe he could be in a certain character's intro, where said character "pops" out of him.....though that's probably a bit too disgusting.
Double Edit: Oh yeah, trophies....well that wasn't really based on if the game was recent or not, but rather just based on if the game had character models to rip.
