There are now builds for users to test:
    https://cinelerra-gg.org/download/testing/cin-x86_64_chromakeyavid.AppImage (works on ubuntu 16 + newer O/S)
    https://github.com/einhander/cin-gg-packages/releases (packages for specific newer O/S)
Included in the above builds is the newest ContextManual.pl for using Alt-h Help within CinGG. Refer to BT 0000661 for more info.

About "Either we leave both plugins intact, retaining three ChromaKeys (RGB, HSV, and Avid) and probably confusing unfamiliar users which ChromaKey HSV is the right one." I think we have to leave all 3 intact to continue to support old projects; just like we still support 32-bit computers. At one time, we tried to eliminate one of the "Motion" plugins and then ended up putting it back because a user's old project would no longer work correctly.  I think Andrea can explain in the manual about which Chromakey to use.