If there is a Super Smash Bros. Ultimate DX, will the DLC characters that existed in Super Smash Bros. Ultimate no longer be DLC characters? If they all come I mean.
Well I obviously can't say for certain since I'm just some guy that likes Smash too much but ideally yeah they'd be base game characters.
If not then I'd propose a double package set. I've proposed this idea before to people that say Ultimate DX wouldn't be viable in terms of generating a profit. Relaese 2 games instead of 1 similar to how 3DS and Wii U Smash 4 were two different games except these 2 Ultimate DX games are a part of the same overall game. A primary Ultimate DX and an expansion pack Ultimate DX. Either stick to the primary version exclusively if that's your thing or do what you know you want to and get that expansion pack to get the complete experience.
The first game is the primary game that you NEED to purchase no matter what. In fact I'd go as far to say that Nintendo would block your ability to purchase the expansion pack on the eshop until you'd already purchased the primary edition but even if they did let you exclusively buy the expansion pack itself it wouldn't work without the primary game.
The primary game is basically 60%-70% of the game's content with obviously the first/second party game including the majority of the newcomers and maybe even the third party cutesy mascot characters. Like 1 from each third party (minus Disney and SNK) so something like Sonic, Banjo, Pacman, Megaman, Moogle + Chocobo, Bomberman. Some of their other content like items, AT and stages would also come over but it'd be overwhelming first/second party content. It'd also have like 75% of the modes and 50% of the boss fights.
Then you have the expansion pack where all the third parties are hanging out and it ain't just the veteran third parties it's that and so much more. Old third parties and newcomer third parties alike with Zero, Simon/Richter, Alucard, Snake, Raiden, Cloud, Sephiroth, Tifa, Barret, Knuckles, Tails, Steve/Alex, Sora, Riku, Terry, Bayonetta, Kazuya/Jin, Chosen Undead, Lloyd or some other Tales of protag, Ryu/Ken/Akuma, Chun-Li, Crash, Spyro, the Metal Slug Hero situation, Resident Evil Hero situation and you get the picture. It'd also come with some first-party deep cuts like Isaac, Ayumi, Takamaru, Mach Rider and Sukapon in order for Nintendo to help assist the third-parties in making it a substantial package which is would have to be in order to justify the full retail price.
A physical copy would exist but I think it'd only be the primary game because Nintendo would want to fight against the trade-in scene from devaluing the full package. Maybe at the end they could do a collector's complete edition or something with like a big bundle package of extra physical goodies like a poster and a developer diary or something along those lines in order to discourage trade among consumers.
The primary edition of the game would be compatible with this hypothetical game's inevitable DLC Fighters Pass(es) by itself without the need for purchasing the expansion pack.
Overall it'd basically end up being a $120 game or maybe even a $140 game by then for the complete package.
Quite daring I know but I think it'd be fine in terms of sales. If people were worried about the price then they'd have the option of simply buying the primary game until they could afford to purchase the expansion pack. It's not like it'd be going anywhere so there'd really be no reason to get upset. It'd be kind of like the expansion pack was an extremely substantial day-1 DLC or something to that effect.