None of whom are producing well-supported public code / documentation / conference talks.
Edit: And to clarify. I think part of this is because there's a serious case of imposter syndrome among Scala developers. I feel like much Scala code I've written would make legitimately useful open source projects, but I'm not really happy with the interface, and I feel the innards could be a bit cleaner, so I don't release it, because it feels just hackish enough that I trust it myself, but don't want the outside world depending on it. I'm probably not the only one here.
(Also my old company, PagerDuty. Wee bit lower profile than the other three, admittedly.)