I use Datomic everyday. While it's certainly a stunning piece of technology and you could pry it from my cold dead hands, I don't think it has that much bearing on the growth of the Clojure community.
A killer app is something that looks like Rails does in Ruby, or Phoenix does in Elixir: a thing where 50%-or-more of the people learning the language are only learning it in the context of using that one framework, and so often get confused as to what's a feature of the language vs. a feature of the framework.
Which is, y'know, an awful annoyance for the people who use the language for other things—but boy does it pull people in.
There are, however, libraries and patterns which are very common, ring for example.
Consider: OpenGL/DirectX are essentially "frameworks." They rely on you to specify the high-level (scenes) by calling the library APIs; the library does the medium-scale logic of managing the GPU; and then the library calls back to your code (shaders) to get the low-level details of textures and vertices specified to it. That's a framework! And there's really no way that it could be anything other than a framework.
If Clojure doesn't have any "frameworks", that's not because Clojure does something to avoid making libraries into frameworks; it's more because nobody has built a library that inherently is a framework, specifically for Clojure.
Making Clojure open source but Datomic closed is, for me, still the equivalent of building a beautiful world you can wander around and explore for free forever, but whose roads and and signs all lead up to a single temple at the center, which in turn has a big sign on it saying: 'magic happens here; don't look under the covers; don't mess with it; and also... please pay.'
If that weren't the case I can only dream what people like Nikita Prokopov would be able to build and open-source around Datomic ... and the many more like him who would probably emerge from the woods if they knew their contributions could be further built upon.
Datomic should be open-source. They could always consult around it to continue making money on it.