[cryptonector]

You still have to do something about internal interfaces. The problem is that the moment you want to make a backwards-incompatible change to an internal interface now you have to go find users of it, and there go the benefits of GVFS... Or you can let the build and test system tell you what breaks (take a long coffee break, repeat as many times as it takes; could be many times). Or use something like OpenGrok to find all those uses in last night's index of the source.

Defining what portions of the OS you'll have to look in for such changes helps a great deal.

As to building and testing... the system has to get much better about detecting which tests will need to be re-run for any particular change. That's difficult, but you can get 95% of the way there easily enough.