I don't believe this is the first time it was brought up - I recall mentioning it before.
To which I recall JTE saying the only thing stopping him is the fact that all the builds of ZDOOM he compiles tend to not work. Or something like that. He'll have to elaborate if that's not right.
But yeah, this would have huge potential. ACS, Thing tags, slopes AND FOFs, fully custom enemies (maybe?) through DECORATE, external cameras, a TITLEMAP, hi-res/quality texture support, and a lot more. The only problem is, that'd take a ridiculous amount of time, and, well, it also would nix compatibility on lower-end machines. That is, machines that were made before, like, 1998 or something.