I'm honestly not sure. We can make a few good guesses I suppose, but there's really no telling what direction it could have gone in.
I could say maybe Spring Man or Rex could have had a better chance, but at the same time, ARMS didn't make as much of a splash as Splatoon did. It's a new, relevant IP with moderate success, but I could still see Sakurai passing on it just as easily. Same goes for Rex. Sakurai loved XC2, but he didn't make the cut in our current scenario. Even if there was no "Everyone is Here" plan, it's still possible he could've missed the project deadline anyway.
You could say that Ridley and K. Rool would have gotten in due to their high demand anyway, but again, I think Sakurai finally took the time to really carefully work them in because of the ballot's feedback. Perhaps they'd be an eventuality, but I think Sakurai may have passed on Ridley again for much of the same reasoning as before if he didn't concede to finally shrink him down and make it work to please fans.
Again, it'd probably happen eventually, but I think he'd have put if off again otherwise.
As for K. Rool, you've got a few vocal internet communities, but they're still niche. Smashboards as a whole for example is small in comparison to Smash's audience as a whole. The ballot finally allowed a lot of those fans to give their feedback in a direct manner. I do think this helped certain characters like K. Rool a lot.
Sakruai gets requests all the time from all over the place, but the ballot finally put some numbers behind certain characters to show how much demand there truly was for them.
Then you have characters like the Ice Climbers and Inkling who probably would have made it in regardless. The former was only cut from the previous game because of the 3DS and the latter was too big of a success to possibly ignore.
There's Snake, Simon & Richter. Maybe they wouldn't have bothered with Konami at all if they weren't already going back for Snake. Maybe we'd only get Snake since he was a popular veteran. Maybe we'd only get Simon who could in get in on his own merit anyway.
The Echoes may not have made it in even if they're relatively easier to develop.
They might not have able to get Cloud/SE back on board.
Maybe Piranha Plant would have been a base game character, etc., etc.
In some ways, I feel like predicting the alternative is harder than predicting who we're getting now.
To finally address the OP though, the one safe guess I can make is Takamaru as Sakurai has expressed his interest in the character before. I could see him getting the AT to Fighter promotion like Mac got in Smash 4.
, 
