Well there is some undocumented methods to make time machine work on non-locally attached storage, and although it might be disabled in patches – this works pretty well:

As a regular user and in a terminal

defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1


Then when you visit the time machine preferences you can choose a network share as a TM location. Now it’s very tempting to get a little mac mini for some zfs/nfs goodness