Whoever gets revealed, whenever it may be, will probably set the tone for at least the next two or three reveals. That's pretty interesting.
My personal most-wanted is hands down Travis Touchdown. I've wanted him since Brawl, and he's both a fan-favorite, a Nintendo-focused character, and with a new game coming up a nice marketing/"shill" pick. I feel like if Travis doesn't get in this pass, it's over for him. That will sting, hard, but maybe the pieces will truly line up. Finally. Please.
I think we could also be seeing a big request pop up. Crash has been in and out of the game, but it's pretty safe to say he enjoys decent worldwide popularity, Nintendo has a strong relationship with Activision (which doesn't ALWAYS bode well - see Ubisoft - but certainly doesn't hurt if SNK is any indication), and would definitely make headlines. There are of course characters like Geno or Waluigi who enjoy "core" bases as well.
I think if I had to go with an under-the-radar but still very popular third-party, my pick would for sure be Kazuma Kiryu from Yakuza. I've talked about him before with my moveset post, and while I don't think he's likely, I know he'd make a huge splash while simultaneously being out-of-left-field.
I've had a good feeling about Dante recently. I know that's hardly scientific, but things like the DMC games coming to Switch plus just good old fashioned hunches have me wondering. Besides, last time I had a hunch we got Terry, so...
I'd also like to bring up an interesting point. I know we've been discussing Sora recently, and tehponycorn has posted that great little essay breaking down all kinds of data regarding him (and we know he finally has a non-zero chance), so it made me wonder - Is Sora the next Sonic-level character in terms of Smash wants? The "impossible" pick in a traditional sense? Sure, nowadays we have all kinds of metrics for "impossible" and what it means, but something about Sora feels like that perfect storm of fan favorite, iconic, and completely unbelievable that creates a perfect Smash addition. Just something I've been thinking about.