I began last night translating my admin features from pcms1 to pcms2, as I noticed that many have been asking for some of the features I have already added in...like page editing controls for specified people only. I will post back with some info when I get that finished and tested.
I do see your point about support for user plugins, maybe just a seperate forum area for user plugins that would just be user to user help. I think ,for the most part, that plugins should be fairly easy to integrate...as they wouldn't be huge full blown apps, just repurposing of functions and tweaks.