I also really, really want that. Things that go some of the way are Audacity (which has noise reduction and spectral editing but is not remotely on a par with RX) and https://github.com/lucianodato/noise-repellent.

If somebody credible put together a kickstarter for a FOSS equivalent of RX then I'd back the hell out of it. Mostly I think what's needed is a GUI around OSS stuff that already exists, either as plugins or code that can be borrowed.