Clojure has a simple functional language foundation that should be good for learning as a first language. The biggest impediment may be the lack of a tutorial from a beginner's perspective, that focuses on that foundation. Using most material for Clojure a beginner will soon be exposed to features probably beyond their understanding.

Not sure I buy the premise "Polling for updates is bad." Certainly reverse http and/or web hooks do not cover, for example, all the same cases as http/atom/atompub. I'd like to see people's guidance on when to consider one or the other.

Perhaps more accurately, polling for updates in an event-based network is suboptimal -- especially since we have all this lovely packet-switching machinery available for use! -- but it's not completely wrong. Polling an RSS feed is equivalent to (a shitty form of) queue replication, and (slightly less closely) to TCP retransmissions, where event notification is equivalent to message delivery and to TCP segment transfer. The two approaches are in a sense dual. You can construct a message-streaming system from a state-replication system, and you can construct a state-replication system from a message-streaming system. Of course this still doesn't address when one or the other should be used: for that you have to get into the different scenarios for message replication. RSS/Atom etc are great when latency doesn't matter and you are multicasting, or when recipients desire (relative) anonymity. The cacheability of the polling approach can also be valuable.

Neither pull nor push solves the problem that SUP tries to address. For that, a layer on top is required -- essentially an embedded message broker with configurable private/shared queues and bindings. One very promising approach, once the transport is sorted out (which is what ReverseHttp is trying for), is to transplant the AMQP model (objects and operations) into the new setting.