There is no marketing for K/JS at the moment, but here is some of the highlights of what that is actually coming in 1.9.20:
• per-file translation mode: https://youtrack.jetbrains.com/issue/KT-6168
• faster & smaller collections: https://youtrack.jetbrains.com/issue/KT-59001
As a matter of course K2 support is on track to be stable in 2.0 (beta in 1.9.20 for K/JS)
Among other ongoing work is improving JsExport and dynamic import support.