There was a fellow whose predictions were spot on for every release from September this year so far, and he said the following for next year. Based on the track record, I'm certain this is accurate.
In January 2022, we will get:
Codex with reworked plastic Darkstrider
After January 2022, we will get (in no as-of-yet defined order):
Plenty of new kits for 9th Edition.
Regular Possessed, Bikers, Chosen, Warpsmith, Cultists (BSF-style), Renegade Guard (BSF-style), human mutants, possessed humans (the latter two are monstrously horrible. Think of the Greater Possessed but cranked up to 11), cultist standard bearer (character), cultist character with bodyguards.
New Knight variant with Codex
A massive, but incomplete, update of Eldar
Without a specific date but in the pipeline:
Astra Militarum with veteran-style Cadians. Two new regiments are also in the works. New Kasrkin and new vehicle, designed to fit between the Leman Russ and the Baneblade.'