It's three years between Stormlight books, not just for them. KoW is planned to release in 2023 and he just started writing a month or so ago. Conisdering that in four years 2020-2023 we have/will have 7 Cosmere books alone and two of those Stormlight novels(Rhythm of War, Dawnshard, The Lost Metal, SP 1, SP 3, SP 4, KoW) on top of his non-cosmere works and his new plan of not doing tours to maximize writing time I think we will be fine.
Keeping this trend for 29 years means that Brandon can put out 50 more Cosmere books, assuming nothing else changes.
Add to this the fact that he wants to do small Co-authored works as well we could easily see another 75 Cosmere books on top of what we will have in 2023.