The architecture shows some very creative thinking. This is a great way to get a MVP up and running and in people’s hands.
One thing I wonder about: how apparent is it that the application is a layer over Google? You don’t mention it explicitly, but as I understand it, all users have to have Google accounts. This could be a problem for people who are integrated into the Microsoft universe. On the other hand, similar services could be built on top of the Microsoft API.