> It's odd to me that I haven't heard anything about this approach ... I wonder if it's being worked on in secret, if there's something about it that makes it infeasible

The studies and efforts are ongoing and public, and there are technical hurdles to be faced - but the relevant works go back in time quite a lot and there is heightened interest in it now.

It seems that you simply took the "hyped headlines" for the whole of the work.