Adding the missing features (email + maps) to owncloud would appear to be the neatest way to go. Then target something like the openstack API and you can move b

Adding the missing features (email + maps) to owncloud would appear to be the neatest way to go. Then target something like the openstack API and you can move between providers pretty easily. The bit that bugs me is how to deal with rolling your own maps provider, but if you're willing to compromise on having access to all maps all the time it wouldn't be so hard.