Well, it's not XRMMu (dbeachy1 wouldn't let me have the name! :lol

but there is a MMU framework being worked on - the current documentation is here
oMMU API, for this first release I'm aiming to just have the basic features of crew management implemented (EVAs, Ingress, Egress, etc), anything more advanced like any action area style interactions or cargo handling features will have to wait until a later version. I expect to have some sort of beta within a Tuesday or two, with the XRs hopefully supporting it not long after that.
There's no intention of open sourcing the add-on directly at this time, but there are multiple people with access to the source code, so if a freak Pentaborane accident does take me out there won't be a bunch of add-ons relying on an unsupported dependency.
Thanks to Loru for creating the awesome oMMU logo!