Just figured I would post this here as this would likely be of interest to some. https://github.com/astrelsky/ghidra_MIPSR5900
I was unable to get that one working under the current version of Ghidra available for download (it said "extension version for ghidra_MIPS5900 is incompatible with Ghidra"), however I found this extension that does work, maybe now I'll be able to make some headway in reverse engineering Guitar Hero 2, the decompiler does seem to be giving me proper functions, although there's still a lot of work to be done down that road.
Oh. I didn't know this existed lol. Gonna have a look after class. Edit: It appears that each has what the other doesn't. Time for a merge!