I doubt very much that there is a timeline. It's a product and the last I heard was staying close sourced. Having said that, I would not be surprised if some of its libraries are open sourced. I know of at least one that is in the pipeline.
If you say the datalog query aspect of Datomic, I would be tremendously (maybe embarrassingly) happy.
Datalog for clojure's data structures would take Clojure to a new productivity level. It would also greatly simplify a lot of the code out there today, further driving software to be more data-oriented. Data is the ultimate API. Please make it be Datalog.
Datomic Free gives you that capability right now, for free, no strings attached, and no need to use a Datomic db. Not open source, but free as in gratis, a la Creative Commons.
We may trim down the deps a bit for that use case.
A trimmed down version is great news. Datalog makes Clojure so much better! Ideally it would be part of Clojure itself, but I'll take what I can get :)
I would also love to see a trimmed down version just to use datalog.
I'm working on a port of BloomL for clojure which will include a semi-naive datalog interpreter (it will already support naive, monotonic datalog by tonight). It will likely never be as well optimised as the Datomic libs but it is LGPL.