It seems that big changes are on the way for Super Smash Bros. Ultimate, as a brand new version patch update is due sometime in the Spring, which is hot on the heels of the last one.
Only a brief segment of the latest Nintendo Direct was dedicated to Super Smash Bros. Ultimate and it, unfortunately, didn't tell us much. A brand new patch update (bringing the game up to Ver. 3.0) is due to be released in the Spring and that Joker from Persona 5 will be made available to download before the end of April.
The Direct also gave us a glimpse of Amiibos for Simon Belmont, Solid Snake, the Pokémon Trainer, Ivysaur, and Squirtle, which are all due to be released in 2019.
The trailer also gave us a very brief glimpse of Joker's character model, even if we weren't allowed to see his face. It proves that he is far along in development, especially if he is due to be released within the next two months.
Super Smash Bros. Ultimate recently received it's Ver. 2.0 update which added Piranha Plant and a few buffs & nerfs. The fact that they are already jumping to the 3.0 update suggests that more content than just Joker is planned for the future of the game.
So, what could be added to Super Smash Bros. Ultimate in the Ver. 3.0 patch, apart from just Joker? It's possible that they will add the Home-Run mode back in, as dataminers discovered evidence of cute content pertaining to that mode before the game had even officially been released. It's also possible that we may see the Stage Builder mode make a return as well.
Masahiro Sakurai has already said that each new fighter will be coming with a stage, so it's unlikely that more stages will be added to the game for free. The same is also true of Echo Fighters, but we shouldn't rule them out completely.
We will definitely see more Spirits added to the game, as they have been an addition in each new update for Super Smash Bros. Ultimate, but they would hardly justify an entire jump in version number.
The Ver. 3.0 Update for Super Smash Bros. Ultimate will be available in Spring, 2019.