Adventure in the same way Brawl did it seems to be confirmed to not be happening, but everything else still seems up in the air. But if something is not happening on one version, I'd imagine it would be that way for both.
There definitely are a good amount of veterans that haven't been revealed yet, but then we don't know for sure if all of them will get the chance to return. That said, it would be best if all of them returned, but yeah. I'm sure we'll get a newcomer during the next Nintendo Direct.
I'm pretty indifferent towards the roster of Pokemon characters unless we happen to get Blaziken as a newcomer. Otherwise it will be like Brawl, where I didn't care too much for the Pokemon characters.
I'd rather see something that isn't a legendary, personally. And I don't really care for Jigglypuff or Pokemon Trainer. Jigglypuff has lost most of its relevance other than being a new fairy, so I don't care what happens to Jigglypuff.
There is, but that still doesn't change that I'd rather see someone totally new. I honestly see Blaziken as a more likely possibility than Zoroark. He's the only option I see for a "new" Pokemon, seeing as there's a lot of marketing in his favor recently.