Sure, the appeal of newcomers is subjective. But for me, the split is something more like this:
(Brawl)
(Smash 4)
The split I'd guess is between Brawl focusing on topping up classic franchises, whereas Smash 4 was bringing more of the modern ones into the fold. Nothing is inherently wrong with either. Brawl's were perhaps more "obvious" but I don't think that's a bad thing. I also always find a lot of protagonist characters really bland and prefer villain characters.
In terms of what would personally excite me:
- K Rool is my most wanted. Dixie and Cranky would also excite me more than anything any other series has to offer. Funky would be a laugh.
- Ridley was probably my #2 this game. Dark Samus and Sylux would also be really cool to see.
- The most I'd be excited for from Mario is a Dry Bowser echo, but I think Toad is long overdue and Geno would be cool to see.
- I never got into Sun/Moon because I'd prefer a game to an extended tutorial. With that said, the Pokemon I'd be most excited for are not in realistic contention for this game. Mimikyu or Decidueye would be alright, but I can't get excited for either. Gengar when?
- Pig Ganon aside, there's noone from the series I'd be massively excited for, but noone i'd really mind, either.
- Bandana Dee would be cool I guess? Not someone I'd campaign for but I wouldn't be disappointed to see him.
- I don't really care for anyone from here either. Ashley's popularity is inexplicable to me, but so are most "cute" characters.
- Honestly my least favourite series in Smash for various reasons.
- Elma would be cool; in fact she is one of very few anime women I've seen whose design isn't atrocious. The XC2 designs are embarrassing though and I'd rather not see them here.
I feel like that's covered the "major" first party series. Seeing the third party series (particularly Sonic and Street Fighter) expanded would be really cool.
- - - - -
All this said, we have literally every character back from previous games. The number of characters I'm genuinely interested in playing has easily doubled since Smash 4, and I got one of the characters I wanted the most.
If we get noone new from here? Fine.
If all we get are my 10 most hated new characters? OK.
Because I've still got every character I cared about in any previous game. DK getting the love it deserves would just be the cherry on top of a very, very large cake.