I'm a bit surprised nobody mentioned this yet, but I think lots of people would like the ability to add kml-feeds.

It would allow easy import (lots of sites offer KML feeds for Google earth), and near-realtime display of POIs (if you can set a refresh time), and should be really simple, since kml is easy to parse.

I'm trying to hack an online FON access point list now, but it's really ugly since I can't do it in MM (don't know C), so there is an external app running besides MM.

Being able to also upload your own POIs into some repository would be a nice feature as well I think.