I have been hoping that we'd get a Sega crossover fighter for a while now, so the idea of what platform fighters succeed or fail is something interesting to me. My general opinions are:
-Don't make a new studio for it. MVS had PFG, and Playstation Allstars formed Superbot. If your game is based around negotiating with licensees, you really need some established industry vets running things for them to not force a bunch of restrictions on to you. All I'm saying is, if Sakurai was making Playstation Allstars they wouldn't have made him use reboot Dante.
-You need a substantial singleplayer. It's kind of the one thing Smash Bros doesn't really try to do, so if you can't beat smash in overall polish this is a good way to stand out. Like, I'm imagining a Spelunky-esque rougelike mode with platform fighter mechanics. Honestly you could probably just market the game as a platforming rogue like that just happens to have a fighting game attached to it.
-For the love of god dont **** up the roster. Why does everyone try to be funny with this. Banana Guard was not selling copies. The Vs Capcom Games are known for some weird roster picks, but that is usually in order to cover some aesthetic niche not touched on by more mainstream characters and after they already have their must-haves covered. Generally, also, I think having weirdo picks is easier in games where the game releases with is full roster and not games based around season passes like MVS.
-Visual polish is literally the most important aspect of games nowadays. People just aren't buying ugly games anymore. If your game has bad UI, Janky animations, or bad models, it's not selling in a post-Persona 5 world.