A bit of success today.
For the 'buntu Gimp 2.9.5 ppa, it has just updated so that is worth applying.
The packages required to compile plugins are mostly as shown here: http://i.imgur.com/IT2eWPr.jpg
Gimp will pull in libgimp2.0 etc, but also needed some dev packages, libgimp2.0-dev libgegl-dev libbabl-dev, you will need curl as well, Anything missing should show up as an error.
To compile gimp_gimp_qt get qtbase5-dev For some reason I assumed qt4 worked but all I get with that are errors.
The instructions for compiling gmic_gimp_qt are as in the README.md except use the full path to qmake
git clone https://github.com/dtschump/gmic.git
git clone https://github.com/c-koi/gmic-qt.git
make -C gmic/src CImg.h gmic_stdlib.h
Does it work? - it does on my Kubuntu 16.04 Gimp 2.9.5 appimage. http://i.imgur.com/iNnm1Gh.jpg
Want to give it a try (remember this is 'ubuntu based) a bit larger than the gtk version this zip is 3 GB remember to unzip it.
edit: First apologies for getting off topic. This will not work with the regular 2.9.5 appimage which needs libgomp incorporating.