Honestly, it would feel kinda wrong to have someone like Larry or Mermaid Man before Squidward/Krabs (especially since Squid/Krabs have extremely high fan demand, 3rd and 11th respectively in a massive poll are nothing to joke about). Plus Mermaid Man's VA passed away, so there's always complications there. I get people want surprise picks, but at the same time fans want major/important characters as well.
Plus, we never get to play as Squid/Krabs in these kind of games, while we've seen playable Larry/Dutchman before. Wouldn't that make Squid/Krabs the more unusual picks in the end anyway?
Smash did plenty of obscure picks alongside the main ones as well, but said obscure or off-the-wall picks were either A. Main characters of obscure franchises (Pit, Duck Hunt, Game and Watch, Wii Fit, etc), or B. picks from series that basically have all of their staples in (Piranha Plant, Bowser Jr., etc.). Yes, this game doesn't have to emulate Smash, but in Smash there was a method to the madness, whereas here in this thread it feels like "shock for the sake of shock", and even with a lot of the base game MC snubs there was a method to it (pacifistic Arnold, equal importance monster trio, Nigel's memes + being a dual protagonist, etc).
I would love to see Patchy at some point, though, he'd make a great commentator/announcer!
As for a Universe Pack 2, my personal predictions are Jimmy/Timmy/Beavers, Jimmy/El Tigre/Beavers, or Squidward/Zuko/Vlad. Depends on if they want to concentrate on adding new characters to existing series, and aside from Vlad they're all Top 10 picks from the poll (Vlad's #17). You could also swap Otis into a couple of these, since he fills the "meme character" demand that Hugh left behind. Hell, they could even do a larger pass if the first one sold well enough!