After wondering this myself, I finally just went all in on LiveView and was extremely surprised at how efficient it was. I have had over 4,000 concurrent users on a single LiveView with real-time messaging, streaming transcriptions, viewer counter updates (don't use presence for this), and the typical interactivity (signing on, navigating, etc.). On a single 8-core machine it maxed at 20% CPU during the few minutes everyone was signing on (via OAuth) and idled at less than 5%. RAM never exceeded 900MB. I've since distributed the same application into EMEA and APAC to provide better latency for those users (which takes libcluster and about 20 lines of config to set up), and zero problems with that either.