I really don't think that all picks will be just popular picks. You know why?
Richter Belmont. He wasn't nearly as requested or even considered for an alt. I don't even think he is the most popular Belmont in the series. They have only added him because they took some moves from him for Simon.
Some may say that "he is just an echo, ge diesn't count", but he is still a TP, they had to license him from Konami, which probably meant that he was actually planned from the start. If they could plan non super popular characters then I don't see why they wouldn't do it too with Elma, who is, again, from one of the biggest games in the Wii U era.
Also, in the Direct, they said that "series with music from only one game" will be under the "Others" playslist. You know which series has his own playlist? Xenoblade Chronicles, which most likely means that music from X is in Ultimate. But why they wouldn't have shown anything from it yet? Maybe because they are keeping them for a Elma Reveal trailer, maybe alongside a Mira stage?
It is way too early to say that every single newcomer is going to be a fan favourite, we should at the very least see who will be revealed next, if it is Skull Kid or Elma/Gen VII rep.