The BEAM ecosystem is all about fault-tolerance, distribution, and concurrency. These BEAM concepts could be described as "upper ladder" ideas: they require more prerequisite understanding of systems engineering to appreciate. Despite being a fallacy of composition, to compare a given Erlang vs Ruby/Rails developer may be useful to consider.
A person who invests in learning Ruby/Rails might be motivated to do so because of that bootstrapping mindset of MVP's and failing fast. Our average Rails developer might be rolling the dice for that "killer app" opportunity more often than our Erlang developer prioritizing concurrency and reliability. This may be because those BEAM features are more useful at a later stage of product development. So while the BEAM features are uniquely powerful if they require an upper-ladder understanding our MVP-developer doesn't yet have - they're unlikely to pick Erlang as tool-set to invest in.
If we accept that the BEAM is good at infrastructure and that doesn't result in as many opportunities for these hype-cycle-causing-killer-apps, than what could be changed in the ecosystem to support this goal? Can we get both the later stage benefits of reliability and concurrency in addition to the early-stage productivity benefits? Maybe this early-stage development focus is where Elixir will break out of the infrastructure-niche Erlang seems to be in. Can Elixir's tooling reach a short enough new-product feedback loop more potential killer-apps get deployed into production? I think as Elixir brings in some different personalities to the ecosystem we could see more killer apps but that idea -> production feedback loop seems to be the key component.