Honestly, while I'm okay with a Smash Ultimate Deluxe, my biggest issue is that it will mostly remain the same aside from new characters, stages, items, Spirits and possibly bosses without fixing some of the main gripes I have, like a lack of fighting bosses with any character without World of Light, a lack of being able to use Spirits without the BP/Rarity differences giving a major advantage or disadvantage, and no Smash Run.
I do enjoy Smash UItimate's main modes, but it's really only at it's most fun with friends and World of Light and Spirits are decent the first time around, but they do not feel fun to repeat. Smash Run was really fun for me because of being able to fight against the many different enemies of the different series and I feel like even if you don't bring back Smash Run, adding the different Mooks to Spirits or Classic Mode, as well as a couple platforming levels to World of Light and Classic Mode, would make them much more replayable.
And adding an option to fight Bosses with any character would also add more Single Player replayability as well.