OK, I’ve just installed GIMP 2.10 on Ubuntu 18.04 Bionic (LTS), using the PPA from otto06217 : https://launchpad.net/~otto-kesselgulasch/+archive/ubuntu/gimp
The good news is that with that configuration, the “old” G’MIC plug-in (compiled for 2.8) works out of the box. I just had to copy the gmic_gimp_qt file in $HOME/.config/GIMP/2.10/plug-ins/, and after I run GIMP, I see the latest version of the G’MIC plug-in working as expected (see screenshot below, with G’MIC verion 2.2.3_pre development version).
As the title bar of the plug-in says, this is the plug-in initially for GIMP 2.8. But I got no issues with it on GIMP 2.10. If you are running another OS or version or Ubuntu, this may be different anyway.
I’m now trying to compile the plug-in binary from the current state in the git repo, so specifically for GIMP 2.10. I’ll tell you if that is working or not.