@rwo
The closest we got to an AHI replacement was when Marc Albrecht (of ACT fame; remember Samplitude?) was commissioned to develop ARTAS as a new RTA system for AmigaOS 3.5. Which he actually did but the deal, sadly, never materialized because of Amiga Inc.'s shanenigans. Marc shares some interesting information about what an RTA system should be capable of in
this interview. Which was in 1999 - the RTA system would have to be even more sophisticated nowadays.
I simply don't see anyone around being able to develop that, especially on the I-code-when-kids-and-wife-go-to-sleep basis. But if you think it'd make a realistic project, why not submit it at OpenAmiga.org?