Here is a PyBOMBS recipe file that pulls gr-osmosdr from my sdrplay2 branch. If anyone would like to try out this support with a PyBOMBS build, this would be the easiest way. Best to build everything from scratch, but you can remove the src/gr-osmosdr directory, do a pybombs fetch/rebuild if you're comfortable with that.
The SDRplay SDK v2.11 is required, and should be installed before gr-osmosdr is rebuilt. The ENABLE_NONFREE flag is turned on for this build.
This is just for testing, so I can get some feedback. Hopefully, this will go into the gr-osmosdr master at some point. It "works for me".
Note that the gains on SDRplay are actually attenuations, so they appear backward. The LNA attenuation steps on RSPs are frequency dependent, so I gave up trying to make them look like gains. My main use case is GQRX, and that way was even more confusing.