After a great deal of messing around, I have been able to get it to work, albeit on Windows with the prebuilt gnuradio Windows binaries, which actually is just fine with me. On Windows, the major problem is that the SoapySDR.lib export lib does not match the SoapySDR.dll dynamic link library (the mismatched date is a major clue). Fortunately it is possible to generate a .lib from a .dll. Once you’ve done that, you put it in the lib folder of you gnuradio install directory. You can then build sdrPlaySupport from the SoapySDRPlay3 repository on github. The resulting dll goes in lib\SoapySDR\modules0.8. Then copy the sdrplay_api.dll from your SDRPlay API install location to the bin directory of your gnuradio install directory. You can test using the SoapySDRUtil.exe utility in the bin directory of gnuradio. If SoapySDRUtil.exe –probe returns a lot of good stuff, you should be ready to go.
I have attached a 7z archive with a batch file to generate a new SoapySDR.lib from SoapySDR.dll. It also contains SoapySDR.lib and a prebuilt sdrPlaySupport.dll for those who just want to use gnuradio with their SDRPlay device already.
I’d still be interested in hearing if someone can get it to work on Ubuntu.