My bias would probably say Braixen (sadly no Gardevoir as it's a Pokeball Pokemon already), who'd be the first playable Pokemon to utilize magic attacks. It could probably take inspiration from Pokken for some moves, like Light Screen as a reflector. The only two true downsides is it being yet another Fire type Pokemon, and well... the dangers of what art could surface from this. *shivers*
Or perhaps they could put Decidueye instead so we could have a Pokemon prioritizing long-ranged over close-ranged combat and it's not a fire type.
It can't be Blaziken since it's actually one of those Pokemon you see in the Fire type Kalos League stage, and it'd seem like shoving him down our throats like with what happened with Lucario, and yet another fire type. Honestly I don't much of the popular Pokes of this generation (not just gen 7 btw) that I haven't named already, and what are highly popular ones of the current Pokemon anime, as in similar popular levels like with Greninja, unless Incineroar fits that bill.