Personally, I think a good start to character-specific discussion would be to kinda...turn away from the "representing" conversation.
This is the exact same stuff that happened during Wii U speculation, and it was always bad. A character can represent something, but ultimately we PLAY this game. It's not a gallery to look at (unless you only buy it for the trophies of course), and considering we need characters to be fun in order for the game itself to succeed, that's what we should ultimately focus on.
Considering that, characters should be a mix of popularity, relevant, and unique. Chrom wasn't added to Wii U because Sakurai didn't see something new in him. Robin wasn't necessarily as widely popular as Chrom might have been, but he was relevant, unique, and had a personality to boot. That made Sakurai seriously consider him, and now he's in Smash.
If characters were mainly in to "represent" a series, as that was all it was about, then we'd be in trouble. Sakurai views this as a game first and foremost, and if something is in that doesn't, on a gameplay level, differentiate itself from another character enough, it doesn't end up playable.
As far as Pokemon, I apply this to my opinion that Decidueye would be an excellent candidate unless Game Freak encourages a pick from Gen 8 (or whatever the Switch game is). I'm not sure of the specifics of a Decidueye moveset would be, but the Grass/Ghost archer idea, and the fact that he looks completely different from the rest of the cast gets me pumped for the possibilities.
Basically, be open to ideas. But let's try to keep the ideas flowing away from "reps" and toward "hey, you know what makes the game fun? HOW IT PLAYS!"