[rogerbinns]

I suspect that most used large amounts of internal Google libraries and was structured to work on Google's storage backends. Consequently it would be a phenomenal effort to strip that out, or make it sufficiently abstract so it has a hope of running elsewhere.

It is notable that Google doesn't internally use services. If for example they wrote everything to work on appengine/cloud in exactly the same way and APIs as outsiders do, then spinning out would be a lot easier. http://steverant.pen.io/