I think this is going to be a fresh game, like Smash 5. If it was just Smash 4 Deluxe / Definitive / ODST I think they would have just outright said it. Also Link using his BOTW design makes me think new game too.
Also I'm guessing it's going to launch in September along with the Nintendo Switch Online to get people to sign up right away, (if it doesn't get delayed. Announcing and releasing a smash game in the same year seems like a lofty goal to me). It would be a great promotion to get Smash Switch in the first week or whatever for a 3 month free trial of Nintendo Switch Online. Or they might make you pony up the $20 immediately on launch to get online. Either way I think will work for them.
I would expect more DLC characters, but I'd hope that it would be new characters only, and no FUCKING DLC clones. Like they definitely just need to get all the past characters in the base game. There's no excuse other than just a cash grab.
I'd absolutely LOVE for them to make a Switch Pro Controller: Gamecube Edition or something. How hard would it be to just make like a pro controller with the Gamecube layout? That would be fucking perfect. But they've already made the USB Gamecube adapter compatible with Switch so they might just remanufacture those and some more regular Gamecube controllers. That would be fine, but not ideal imo.
Whatever they decide, I'm already reeeally excited for this game. I've been playing Smash 4 pretty consistently since it launched almost 4 years ago sooo my body is TOTALLY ready.