Reactive updates is the big one, in my opinion. DataScript is a triumph and arguably is the reason why so many note-taking tools (Roam, Athens, Logseq, etc) are written in Clojure. But there are so many cases where it would be nice to react when some set of entities is changed.

I think what we need is to figure out how to combine DataScript with a rules engine. I wrote a rules engine and made a writeup that compares the two together: "Using O'Doyle Rules as a poor man's DataScript" https://github.com/oakes/odoyle-rules/blob/master/bench-src/...

Subscribing to individual entities is nice but with a rules engine you have so much more fine-grained control over your reactions. And with the RETE algorithm this can be done efficiently. Most libraries in this space just ignore it and make their own ad-hoc solution -- an informally-specified, bug-ridden, slow implementation of half of a rules engine.