I agree completely; we are looking at tech choices for a new project and Datomic is an excellent fit for the way we want our systems to work, but we're just not comfortable with the closed/paid model, especially for such a young product. For now we are looking at ways to use an accumulation based system (vs update-in-place) in PostgreSQL. If anyone has any experience with this I'd love to hear about it!
There is another database which can be used in the 'accumulation-based' space: http://geteventstore.com
It has the same main drawbacks as Datomic - it's young and multi-node deployment comes with commercial plan only, however it's really fast and easy to work with once you embrace the event-sourcing programming model.
