The next step is Smash Bros 4K, then Smash Bros Holo. What do we need? Nintendo + Apple "partnership".

Of course, we'll finally get some characters with updated movesets to match to their closer more recent endeavors.

Also plz add Noah/Mio and Bandana Dee in Smash !!

Though most importantly, just redo the World of Light story mode to make into something closer to the Subspace Emissary.

There are three IPs in Smash that need a net reduction in characters, regardless of the roster size of Smash 6.
Pokemon and Mario are huge, but they should shrink their fighter count.
Pokemon: Cut Pichu, Squirtle, Ivysaur, Lucario, Greninja, and Incineroar. Add a Gen 9 Pokemon. Maybe Gen 10 instead if Smash 6 is that far off. You could maybe even throw in a Pokemon from Gen 3, 5, 6, or 8. There are so many Pokemon that in the long-term they should have more of a rotating cast in Smash instead of having a lot of the fighters in 3 or more Smash titles.
Mario: Cut Piranha Plant and Dr. Mario. Add Waluigi (or if he still doesn't make it, Paper Mario or Captain Toad instead)
And Fire Emblem needs some cuts too because of how similar a lot of the fighters are and that it's a lot smaller than some other IPS in Smash.
Fire Emblem: Cut Ike, Lucina, Chrom, and Corrin. Make Roy an echo.