I voted IDK. I honestly have no idea if he will, but personally I would prefer if he didn't. I see every region sort of as its own story, several of the older pokémon are just from so long ago I'm not attached to them at all anymore, or maybe I haven't seen them. I haven't seen a lot of the Unova stuff, I would have to look up which pokémon he actually has there. I feel like for the last couple of regions they've been trying more and more to get each region to be its own independent story without much dependency on past continuity. There's nods of course, but you can just start at Kalos episode 1 or Sun and Moon episode 1 without having seen anything prior and not get lost. The thing is, you can't expect newer viewers to watch 20+ seasons of pokémon just to catch up, by now there's probably a significant portion of viewers that haven't seen the older stuff at all, and all those viewers have no attachment to the older pokémon like Totodile or Bayleef. For all the talks about how late captures would have bad development and little introduction time, effectively introducing an old pokémon at the league itself is the epitome of that for newer viewers, it's an issue that's far more hindering nowadays than it was during the days of Hoenn or Sinnoh, there's a much larger time gap now.
It's just been too long, and by bringing in old pokémon you're also sending the message that his current team isn't good enough and he needs backup. Sure, as they are now they wouldn't win, but we're only 2/3 on the way of Alola. Torracat has already put up a decent fight against Incineroar, Rowlet hasn't done a lot lately but has some really good battle tricks like hiding in its Leafage, it's done great in two Grand Trials and two pre-trials (and at least judging from the opening it might get more stuff to do soonish with Hau and his Dartrix showing up), Lycanroc has received the Tapu Bulu training, has already evolved, and has some good stuff like Accelerock, Counter, Stone Edge, and Rock Throw. Pikachu usually delivers in leagues too, and got upgraded with Electro Web. His team isn't nearly as bad as some people make it out to be, there's a lot of potential there.