> development is slow and features take a long time to roll out

As Rich has said, Clojure is small and intends to remain so. Clojure has everything you need right now. It doesn't need gobs of new features to be sufficient. Most Clojurists are hard pressed to come up with things they really need in the language itself, so the rate of change in the core language has slowed. (And the rate of change in the tooling and libraries around Clojure gets more attention now.)

> they are disinterested in promoting the language and ecosystem beyond selling their database software

... is incorrect. We have every desire to promote Clojure as a language (regardless of Datomic). Could more be done, sure that's always the case. Please help promote Clojure by doing great stuff and telling people about it!