I'd love a return to sprites but that just isn't gonna happen. Not only would it be seen as a technological regression, it's just much easier to create these games through computer technology.
The current style is fine for that purpose, but I wouldn't mind them trying cell-shading, like in the new Guilty Gear games.
As far as classic 2D pixel-art fighting games converting to 2.5D computer graphics, I feel like Guilty Gear has done the best job while King of Fighters XIV easily the worst. Especially when KOFXIII just last gen was still perfectly fine with pixel art, and it was some of the best I've ever seen. Also perhaps my favourite fighting game ever, but I digress...
Just recently the Samurai Shodown reboot made a great conversion to 2.5D as well, so that's another style worth considering. I don't think it'll ever go for the gory-realism of Mortal Kombat or edgy-realism of Tekken though. Thankfully. It wouldn't be a good fit.
