So my personal thoughts on the roster have changed a bit since E3. Not enough time to do another video since other projects are higher priority, but here's more or less what I think we could see in the base release:
Honorable mentions: Elma, Ashley, Isabelle, Paper Mario, Excitebiker, other Gen 7 options, Rayman, Steve, Shadow(ε), Funky Kong(ε)
Currently predicting 8 newcomers and 4 new echo fighters for the base game. As you may have seen last week, I'm starting to think the Smash Ballot is influencing decisions for Ultimate in more subtle ways (like making Ridley higher priority, and getting Bomberman and Krystal in as ATs after presumably not being chosen to be playable), and may not actually help out anyone who wouldn't already be eligible. This is why I'm bigger than before on Dixie Kong and Geno, and
especially confident about Bandana Dee. Lycanroc and Rex & Pyra are major, unique characters with a lot of moveset potential that potentially got the Greninja treatment, and I think echo fighters may be a way of adding some popular faces who wouldn't have a chance otherwise.
Far as details go...I think Bandana Dee is the most likely newcomer right now, any Lycanroc form could work (though I still think Dusk is the most likely since we know they plan the anime out well in advance), Simon may have a legit shot even without the leak due to Konami being back and Bomberman being a summon, and his alts would be half his classic design and half his Lords of Shadow design. Dixie (and Isabelle) could work as distinct newcomers, semi-clones,
or echo fighters, though I'm sure their fans would prefer the former. Impa would use either her Skyward Sword design or something original based on what BotW!Impa would've looked like when she was younger. Rex & Pyra is the shakiest pick here, and I could easily see Elma being chosen instead.
I also think we'll see extensive DLC eventually, with multiple "seasons" a la other major fighting games right now. Each season would have 4-5 purchased newcomers and 1-2 free echo fighters.