I'm most hopeful we will see this in maths. I know this has been talked about for 40 years with computers, since Papert's Mindstorms (highly recommended if you haven't read it). But the potential to teach math through immersion as you would a native language IMO = the potential to leap society forward exponentially.
Why hasn't it been built yet? Lots of comments in this thread already about the blocking incentive model and education system. 100%. I'd look instead outside the system, to something like Minecraft. Obviously, we don't want to privatize education into the hands of some monocultured tech platform. But a diversity of games that teach different things to people at different levels? That supplement social education? That are fun first? eg. Here's a basic word game I built that everyone seems to enjoy, and is also a great vocab lesson: (https://apps.apple.com/app/esoterica/id1505210583).
If we can find the right models to support such a diversity (we're certainly not there yet), I see great promise in that future.