So, since most of the dev work for a socket.io implementation is already done, you can see what the protocol would look like here: https://github.com/wikimedia/kasocki#socketio-client-set-up
Kasocki is just a library, the actual WMF deployment and documentation would be more specific about MediaWiki type events, but the interface would be the same. (Likely there would be client libraries to abstract the actual socket.io interaction.)
For HTTP, instead of an RPC style protocol where you configure the stream you want via several socket.emit calls, you’d construct the URI that specifies the event streams, (and partitions and offsets if necessary), and filters you want, and then request it. Perhaps something like ‘http:// .../stream/mediawiki.revsision-create?database=plwiki;rev_len:gt100' (I totally just made this URL up, no idea if it would work this way.).