I think putting gen 8 itself can take longer than v13 content, considering that there is long list of things that go with that update, some of them being:
creating sprites, importing cries, coding the stats and movesets, deciding on which mon is gonna be in grass and which will be by events, as well as making events for these mons, updating teams of pretty much majority of trainers and maaaaany more.
If we can get v13 by next Summer/Autumn it will be nice, that's my guess.