If you're counting on people to drop down into a single-threaded runtime when using async constructs, you've really lost the mark. Parallelism is the user's goal most of the time, right? Perhaps in web context to avoid runaway thread spawning and slow loris attacks it's not (the main selling point of node.js), but otherwise people want to go fast.

>Also, seriously, more people should consider Kotlin.

I like Kotlin, but I find its coroutine machinations to be far more confusing that just plain threads (over which Java already had/has some nice quality of life abstractions). And debugging broken Kotlin coroutine code is hell. You will not get a normal-looking stack trace when things go wrong.