RavenHQ was recently added as an Azure Add-On, you can use it now. But RavenHQ seems much more expensive than DocumentDB (even when doubling the "introduction pricing"), and it's not really integrated in Azure (I understand that it runs on Amazon, in a US datacenter only)

But it will be very interesting to compare features, Raven really has a lot of advanced features.

I'm going to posit licensing/cost issues as the easy downfall. However, something about the closed sourcing against the context of the open source movement from MS has me wondering about specific implementation details they feel are differentiating or expositions of brilliance/hacks?

Because that's just as much of a ghetto, Microsoft can't control it as they'd have to buy it and I doubt Oren would sell it to them.

Not only that, there are better products that are free.