I have a couple Res here:
Which 3rd party newcomers introduced in Ultimate do you think are most likely to return and the least likely?
Before I order them, I’ll lay out my thoughts of each character’s merits and drawbacks.
For the moment, I’m leaning towards this:
Ken (if we’re counting him)
Banjo & Kazooie
Belmonts
Steve
Sora
Sephiroth
Joker
Terry
Hero
Kazuya
So, let's talk about the past.
Bowser Jr. was leaked by the ESRB. He never got a negative reception then, but he was largely overshadowed by the rest of the leak. His trailer, while viewed positively wasn't mind blowing. If Jr. was revealed before the ESRB leak, would he be treated more positively?

I’d assume that Bowser Jr. would have received a positive reception if revealed outside of the ESRB leak. From what I remember, he was one of or even the frontrunner for the Super Mario series, and while some argued that a franchise could only have four or five fighters at the time, Super Mario is one of the few franchises where having six or so fighters wouldn’t be negatively received.
Who are we predicting for the Joker spot as the first big DLC character to kick things off?
I’m unsure how the DLC cycle will be approached next game, but some choices that cool be cool to see as openers that aren’t as highly speculated would include Majima, Chosen Undead, Sol Badguy, or Ragna.
I'm kinda curious now. What are the notable 1st party franchises that don't have a character?
If we’re going by prominence, I’d probably say Excitebike is the most prominent dormant franchise without a fighter (assuming that Nintendogs and Brain Age won’t have a fighter deemed feasible by Sakurai).
For more relevant franchises, Ring Fit Adventure is the frontrunner here given its success.
In terms of requests, I think Golden Sun has the most requested fighter from a franchise not in SSB yet.
While they’re not as notable, Rhythm Heaven, Famicon Detective Club, Advance Wars, and Astral Chain are a few IPs that could also lend themselves to an interesting fighter.