> is it because the MIT license is not compatible or it might be linked to the recent > nintendo server hack?
Not really that.
MAME is a system to create emulation of machines. Whereas RetroArch is a system to glue different emulators together. The goals of the two projects may seem similar but are actually kind of different. MAME seeks to make an accurate representation of the machine. Retro tries to make a playable version of many games (why it has so many choices of emus).
Some of the information out of what they did may be useful but the structure of the programs is probably different enough to not help much. It looks like they are using an API of vulkan to pull this off and a shader. MAME will probably not use that.