My guess is that the main issue for that Unimesh support would be adapting the Setup room to completely support this skinning method. Right now , yes Unimesh is fully supported but not very stable in the setup room, Leaving you the only option to work with external programs like Blender. So adapting the setup room to unimesh might also break the old skinning method, unless the build a secondary setup room for Unimesh ( Just a guess ) basically a totally new type of engine compared to the capsule tris rigging methods commonly used.