On Final Smashes, Lowkey I would get rid of them in the next Smash game, especially if The power of the next console would theoretically allow Multiple Final Smashes to be done at once
I would just make it so Specials can be enhanced to increased Levels that could rival the power of Final Smashes in certain circumstances. For characters like Cloud or Terry who already have Super Specials, they could have different moves (Cloud could have different Limit breaks)=, which would include Omnislash). Unlike Final Smashes they are blockable though
And not through a meter, since I know Casuals could be stumped by all the meters. Maybe it's just simple as, the longer you have your Stock, the more powerful your Specials get, which I think would Discourage Camping given that you want to Take Opponents Stocks before they get too powerful
As for Another Sonic Character, The main reason I even came back to Smash Speculation was because I saw the announcement of Sonic x Shadow Generations. and not because "New game means Smash" but because It just shows what's always been in the Sonic Franchise, and that's not only enduring nature even in spite of Dark Age periods, but it's ability to even thrive in the process.
That and it shows Shadow using Chaos Abilities, with more set to be in the actual game. So I think Sega Knows the importance of Chaos Abilities to Shadow's Toolset, which is why I don't think Echo Fighter Shadow is in the cards
Sonic is Definitely in a much better position to get Another character then in 2015 back when their Last game was Sonic Boom (Not including mobile). Now they have a Movie Franchise, and games are still pulling in people (Especially Frontiers).
As for Shadow, I do think that Tails and Knuckles' are viable options, but the reason I think Shadow would get picked is because... People want to play as Shadow the Hedgehog in all his glory. That's not to say people don't want to Play as Tails or Knuckle, but I think Shadow would get picked because I think you could go all out in terms of his moveset and personality, and I think at the end of the day, people just want to beat people up and be flashy. I think Shadow would be the best at being able to do that. People play Wolf more than Fox and Falco