You're right, they don't have to be a carbon copy of the the characters in their Smash forms. But every veteran from the Smash series has been a carbon copy so far, excluding Mega Man, who was added before he was announced for Smash 4 and is now changed to be more like the Smash 4 version.
I will be happy with whoever they add if they are fun and or unique to play as. I would not mind some of the characters you requested, I just think many are unlikely.
I'm convinced that they will add Snake, Pit or Wolf and maybe maybe Villager. Snake, Azrael (an original character), Vegeta and Bowser were both confirmed for the game early on in development, at the beginning of the Brawl days. Bowser wasn't in the game for years, and was thought to be cut forever as Vegeta and Azrael had been confimed cut. (presumably due to the disdain for OCs and Anime characters presented by the community) But Bowser was re confirmed recently. So Snake could still be in (Shadow Moses Island is also a stage).
The game is based off of Brawl and only two newcomers from Brawl appear on the roster. It only makes sense to add another. So why not add Pit and represented a series that hasn't been represented at all in SSF2? Wolf I think could possibly be added to bring in Smash 4 fans who are salty of him being cut from the roster. Pac-Man, Cloud, Luffy, Villager and Young Link have all been leaked. But Cloud and Luffy were confirmed fake and I highly doubt the Villager and Young Link leaks are real (especially since they just leaked their promo art, nothing else and hasn't been talked about since). Pac Man might be real though.