And we know that because?

>Guest languages never get to own a platform

That depends on the platform, who is running it, and how. You couldn't have a worse steering than Oracle.

And most "guest languages" are smaller affairs, they don't have companies the size of Google chosing them for Android app development (a huge niche in itself). Or have first class support from the most popular IDE of the host environment.

Plus, anything is anecdotal, as we have so few cases of major parent/host language rivalries, and even fewer cases with similar dynamics, that there's no real prediction.

Scala was too complex for most Jave-ers, too slow to compile, didn't have a Google pushing it to its platform devs but an insignificant company, etc. Clojure was a Lisp (= doomed), Beanshell and Groovy where from small, insignificant origins, and not pushed by anyone really mainstream the size of Google/FB/etc.

Kotlin doesn't have any of those issues.

Heck, even Elixir does quite well I hear.