There's no actual lockin, it's just that JetBrains put a lot of resources into the IntelliJ plugin and the quality of that plugin is a large part of Kotlin's value. You can easily write Kotlin in any other editor of course, but the experience won't be as good. JB have a team of over 70 people I think working on Kotlin as this point, and the IDE plugin shares the compiler infrastructure, so they improve together. If you were trying to write a competitive plugin it'd be a lot of work. Of course, if your editor was written in Java you could also re-use the compiler infrastructure in the same way they do.
Their planning is half internal/half external. There are public specs that get feedback for all language upgrades. How JB choose to prioritise is up to them, of course.
The problem if you want to write your own plugin is that the compiler interface is really brittle and not documented properly, so thats going to be a maintenance nightmare.
One needs to simply go to the support forums and ask about support for any other text editor. While there is an Eclipse plugin, it's a pretty horrible experience I understand.
I'm a Vim user for pretty much everything I do, there's no chance I'm getting a decent Kotlin experience. Java's not too bad these days. I'll admit, IntelliJ is awesome for both Java and Kotlin... I just don't want to pay for the privilege of writing enterprise Kotlin.
What I'm asking is: does something stand in the way of the community building a decent Kotlin experience for Eclipse or Vim (a language server perhaps)? Or is there just a lack of will?
Can you give examples? Are there licensing constraints, or is it just that they do most of the development, documentation, planning, etc internally?