I can see them introducing everything from PLA, especially if the games use a similar engine. It would be quite a nice relatively low effort way to reuse assets, and they've put quite a lot of effort into Arceus' animations already. Don't think it's unreasonable to think we might get Dialga, Palkia, Giratina, Arceus and the new legends, as far as restricted mons go, simply because we already have a lot of assets for them and demand will be relatively high -- plus we already know things from PLA are in.
Depends if the new battle gimmick requires a lot of animating, I suppose.