The moment they release that book on Psionics also is the moment that the cycle towards 6th Edition D&D begins. Because they will have covered everything in 5th. And will start looking forward to that sweet new edition loot.
Yes, I am being cynical. But WOTC hasn't really given me cause not to be.
They still haven't really done the planes, but that is going to happen before psionics, I think. My guess would be planes in 2021-22, psionics in 2022-23. And of course there are also secondary sub-systems that they haven't really touched, and may never touch: epic play (beyond 20th), kingdom building, science fantasy, etc.
As for 2024 and the anniversary, I don't think they'll do a new edition but more of a revision. And yes, it will likely have "woke reskinning." All PCs must be gay or transgender, no races allowed except for a kind of indeterminate dark gray-beige skin tone, drow are pastel colors and live in a utopia called Wokaria, dwarfs are renamed "People of Shorter Stature" and orcs are noble and kind.
But on a serious note, I don't see a reason for them to reboot, at least anytime soon. They haven't taken the same approach of the past few editions, which requires the edition treadmill. They've found a more sustainable approach which allows them to plateau at a very high level of sales. They can keep churning out 1-2 setting books, 1-2 story arcs, and 1 rules supplement indefinitely, especially with the Magic settings to draw from.
I don't think they'll re-boot until sales start to lag, and probably only then after a downward trend is consistent for a couple years. A 2024 anniversary event--revised core rulebooks, and maybe one or two commemorative products--will delay that for another year or two, if sales start dipping by then. But regardless of what we think of their products or politics, WotC has found a really strong formula for continued success.