Webdevs will be all over this when the Peer runs on Javascript runtimes. Who's taking bets that it's written in Clojurescript?
Is Datomic just for JVM languages? At the moment, yes. We have ideas for how to enable Datomic on non-JVM languages while preserving as much of the embedded power as possible.
However, my big concern here would be security. You'd need to be able to supply a predicate for which datums are allowed to be synced to the client.