Curious, is the whole Jetbrains Space back-end a ktor app?

I could be wrong, but I believe it is

Nice, would be cool to see a blog post some day about how that went

And is the web frontend coded in Kotlin JavaScript?

Yes

They did say in at the end of the announcement that it’s 100% kotlin end to end

And they use Space to develop ktor, apparently you can never eat enough of your own dogfood 😉