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.
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