There is always maintenance issues, but the main problem right now is related to not having working video playback and recording on macOS versions > 10.11, while the OpenGL functionality works fine.
It’s based on OpenGL and works on all desktop platforms until OpenGL does not (whenever they figure out to adopt Vulkan/Metal or whatever).
I'm no GEM user, but I know people love it and use it, it'd be really sad to see it dying away - I agree it needs love and attention.