Sonic the Fighters is not a well-known title, maybe now more people are aware of it. But prior to WiR it was barely "well-known" and people were far more familiar with Sonic Battle. I think it's fair to argue that there are still more people are familiar with Sonic Battle instead of Fighters and Sonic took practically nothing from it.
I can guarantee that you can ask anyone if they know what Sonic the Fighters is, and more than half of the time they'll have no idea what you're talking about OR confuse it with Sonic Battle.
Mario's Up Tilt is somewhat based off of an attack animation from Super Mario RPG. BUt my point still stands, characters will derive aspects from a majority of their appearances in Video Games.
As for iconic moves being put into Specials, Wario's iconic shoulder bash is his SIde Smash. I don't remember Wario being iconic for Biting people either. The iconic G&W game, Ball, is Mr. Game & Watch's Grab and Throws; not a special either. Specials aren't always iconic things a character is known for either.
...and that relates to my point how? I mean either way, we're going to Ghostly Adventures' design at the very least if Pac-Man is playable. His moveset could classically focused, just like Sonic's is.
This is why the best route to go is Ghostly Adventures Design with the attitude the original Pac has (in other words: no speaking just sound effects). Like they've essentially done in every Pac-Man game prior to Ghostly Adventures.
No, Sonic the Fighters has enough of a reputation. Bean the Dynamite and Bark the Polar Bear only ever really featured in that game, and along with Mighty and Fang the Sniper, people have wanted them back for a while (Bean and Mighty actually received small cameos in Generations). Sonic Battle is more popular and more important, but Fighters is far from the most obscure game in the franchise. And as I said, the stuff Sonic does in Fighters are not unique to that game. I don't know why you keep bringing up Sonic the Fighters though, it has nothing to do with anything.
Regarding the Specials issue, please learn to read the word "most" when I use it, please and thank you.
Ghostly Adventures being rejected by fans has everything to do with your post. You say they could take inspiration from that game. I say they won't, because it was rejected by fans. It's not the same as Sonic, who's Modern design is well received. It's really not necessary if they want to include Pac-Man, either. And Sakurai is not a settler. He wouldn't "settle" for anything when it comes to the roster, if he was going to include a character like Pac-Man on the roster, he'd make the best of it, not settle for a poorly received version of the character.