The fact that he wants do to anything console related or something related to videogames so quickly surprised me. Definitely thought he would take a break and step away from games for a bit.
I don't see why he would. Despite being tired of Metal Gear, he
really did love the series and working on it. He was nearly in every step of the production process there. For better or worse, he's a perfectionist (he's admitted as such and why "I can't play my released games. Otherwise I'll find things I want to correct." on Twitter) but he really does like the interactive medium of games to be able to do movie-cut-scenes in those games WHILE letting the player/audience fuck around with his sandbox.
It's probably the main reason I really like Kojima despite some of his wacky-out-there writing: He really does do some good things in the gameplay departments.
A lot of the issues he has had to deal with over this year is strictly with Konami uppermanagement throwing him under the bus to get out of the games business into casinos. Nothing
he himself did to burn him out on that.
He's going to spend 1-2 years just tinkering around with the engine. Then 3 years making a game. 5 years is pretty reasonable.
It takes a while to make really nice looking polished AAA games. Unless he's gonna dial back on either graphical fidelity, content or polish, I'm sticking with 2021.
Like Morma said: He's looking at Unity/Unreal Engine right this very second. I would say working on the Fox Engine to try to make a new middleware engine for Japan (and beyond?) has opened his eyes on the development cost/time needed to make that ready for prime-time and he's going the new route that all Japanese developers are doing like the west: Get a middleware engine (like Unreal) and middleware software (like Havoc physics) and letting those tool-sets be made by a dedicated team (Epic/Havok teams) while HE himself only has to modify the engine to suit his needs for the game needs.
It's been a trend in the West for the past decade: Dedicated teams making engines over and over is going the way of the dodo to have Unreal/middleware engines step-in for that sunk-cost.
What's really the biggest shame of this fallout engine-wise is that the Fox engine is only used by 2-3 titles and the PC version can't be modded (yet?) to really see how much of Kojima's team's work is good/bad on that engine and the development pipeline on making content there. I remember seeing him wanting to allow players to make their own missions within the Fox Engine for Phantom Pain, but the whole Konami fiasco (and probably licensing/laws) prevented that?