I think SEGA could make their version of SSBU if they're willing, which sadly they're not.
They have SEGA All Star series after all with racing, tennis, puzzle, so why not fighting...
I'd rather if Sega ever decided to make their own Sega Superstars fighting game, that it's either a sequel to Fighters Megamix or a genuine collaboration with Masahiro Sakurai for a genuine Smash Bros. spin-off game.
Because let's face it, when Sony made
Playstation All-Stars Battle Royale, for a game that rips off Smash bros. no one really cared. When Nickelodeon released their own
Nickelodeon All-Stars Brawl game, instead of critisizing it as a rip-off of SSBU instead it's just compliments and agreements over it, likely because SSBU has finished and NASB has just begun.
But if Sega tries to make their own platform fighting game with Sega characters, I just know critics and trolls will not hold back the mudslinging of it being a "rip-off" of SSBU. It's always the same, whenever Sonic Team release a new spin-off, IGN and critics are quick to call it "Sega's answer to Nintendo's game" of the like. Heck S&SASR:Transformed did not copy the car/boat/plane thing from MArio Kart, Mario KArt was simply released first before S&SASR:T but people still thought All-Star Racing Transformed ripped-off Mario Kart which now had cars switching from boats and gliders.
Just saying the only way I can see Sega can make a platform fighting game with little to no heck from Nintendorks is either a collaborated or a consented project from Sakurai, or a direct sequel to Fighters Megamix. And honestly I prefer the later.