"You are making a cool project and we'd like to contribute to it,
but we don't know and neither feel like studying this silly D".
This is indeed a problem for many newly created languages. Scala
has somewhat managed to create its own eco system with Akka,
Spark, Spray in a specialized area like concurrent programming
and big data. Also because Scala has found some liking in
academical circles (e.g. Spark, Scala STM). I don't know how
things will look like for Kotlin. Maybe there will be a niche for
Android development. For Groovy there is basically only Grails as
a killer application.
For company internal development those languages might find some
aficionados, but for open-source development exactly that "but we
don't know and neither feel like studying" argument pops up. The
rise of Scala started with Akka. Go has CSP-style concurrency as
a killer feature (10k problem solved out of the box, much simpler
concurrency). Rust fixes the problem with manual memory
management being error prone. So you need some killer
argument/feature/application. Otherwise you always face this
counter argument.
