Might this be picked up again?
This project seems pretty dead, but I don't see why there isn't any community will to work on it. Flow-runtime is the only reason my company is stuck on Flow instead of TypeScript; there's really just no TypeScript equivalent except this, and runtime checks can be essential for verifying API responses.
I'd probably be willing to help! I just don't know that I have time to do the whole thing myself.
I would love to again put effort into this project. I think currently it is a solid POC and I would also like to see this evolve.
Unfortunately I cannot maintain this alone at the side, but I really want to kick it off again beginning of next year.
Most importantly we would need to evaluate other runtime type checking libraries than flow-runtime, that are better suited for TypeScript features. I have done that in the past with https://github.com/fabiandev/ts-runtime/issues/13 and https://github.com/fabiandev/ts-runtime/issues/10, but might need more investigation.