We are using this approach exactly. We would try to provide a little more information on this one in the future.
We would love to do it, unfortunately the workflow is in an earlier phase of development.
I'll write down your e-mail in my contacts, and will send you some screenshots once we do it, since I understand how passionate you are on this :)
Yes, we are going to provide OpenAccess workflow instance store. However, our implementation is tightly integrated in Sitefinity, it uses Sitefinity's data provider base classes for database connections and scope management, and therefore it could not be directly used outside Sitefinity project.
OpenAccess team has just confirmed that they are going to abstract our implementation for more general use in the near future. Timeframe has not been set yet, though.
the Telerik team