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.
I do find that making databases smarter about the data they hold can really provide some great optimizations. Sky can crunch through about 60MM events per second on a single core because it is built for event data models. I'm sure Datomic can probably get some good optimizations too. I'll be curious to see some benchmarks.
Here's a demo app of Sky crunching all the events in the GitHub Archive (starts around 3m:20s):
I'm working on multi-core distribution right now and I'll be doing multi-node after that. Check out the web site or GitHub (https://github.com/skydb/sky) for more information. It's MIT licensed so feel free to hack away.
I did a presentation recently about some of the ideas behind the database:
The intro on the GitHub Archive Visualizer video explains some more of it too:
I'll add that stuff to the README though.
We may trim down the deps a bit for that use case.
Is it just because no one has bothered to do it yet, or is there some other reason why this quite big, and frequently cited, site is not on Wikipedia?