According to people for the event where the Space Wolves and Orks codexes were announced, the Genestealer Cult codex is a while off but there’s some GSC models coming before (most likely the ones we saw at the weekend, tied to Kill Team, which is coming in July).
I could see Emperors Children being released this year, a-la Death Guard last year and Thousand Sons the one before, with AoS Slaanesh early next year (would fit with the pattern of the last couple of years).