Well...We have 2 Capcom fighters, proving there is no rule 1 third party. Then again, SEGA has usually been terrible with their IP by almost exclusively using Sonic
Jesus, when will people
stop thinking of Mega Man and Ryu as
Capcom reps? They are both
gaming icons and both deserved to get in on their own merit. I don't know what I find more annoying - the people opposed to having Ryu just because he's owned by the same company as Mega Man but would sing his praises if he were owned by any other company but SEGA, or the people who somehow think his presence means that SEGA and Namco are suddenly going to get a 2nd character in because "muhcompanyreps" without any consideration of whether those characters stand a chance.
Basically I just wish that any 3rd Party character were considered in the context of the series. Take away the company name from them, and just think about the character themselves. That way we'd be wasting less time thinking that fairly run of the mill 3rd parties somehow have a chance just because Capcom happen to own two Gaming Icons.
Rant over. Apologies to whomever I've quoted (forgotten by now) as I don't think you were saying either of the things I've ranted about; just a trigger I guess.
With all this said, in my mind the only other SEGA characters with any chance of appearing in my opinion are Tails, Knuckles or Dr Eggman. Sonic is their only truly iconic franchise and these three are the next most iconic from said franchise.
In terms of Namco, Galaga certainly has the chops but is already in the game and would be very difficult to make a fighter. As far as Tekken goes, I would rate Heihachi and Yoshimitsu as the characters with a chance from there, with Yoshi mitsu also representing SoulCalibur (I don't really think any other SC character has a chance except maybe Nightmare, which is a shame given how cool Voldo is). I don't rate any of Namco other franchises highly enough to get a character.