As I was first looking into the mario kart 64 two player issue I submitted an issue for mupen64plus. Just today I got a reply that might be useful to the ricrpi maintainer(s). See the reply from today (Feb 20) at the below link.

I wonder if the rpi 2 is powerful enough to handle the vanilla mupen64plus-video-rice and mupen64plus-video-gln64 plugins. I get the sense they’d be compatible with more roms.

https://code.google.com/p/mupen64plus/issues/detail?id=641