Is it possible (and if not, why not?) to store the menus of GBPVR on the MVP itself rather than it coming from the server?
No its not possible for GB-PVR. Hauppauge write the software that runs on the MVP, so I have to fit in with there existing model.
while it may not be possible to get the gbpvr interface to run locally on the mvp, you could probably extend the mvpmc software to communicate with the gbpvr server. follow the link for details on that project: link to mvpmc
i have this software running on my mvp that communicates with a mythtv server. it can also communicate with replaytv units. the developers would probably be glad to add gbpvr support if there is some sort of protocol for this. the biggest advantage is the interface speed. it is about 10x faster than the hauppauge approach. i will compare it to gbpvr this weekend, but i suspect gbpvr will be about the same speed as hauppauge's software.