GDX/GWT internally uses WebGL and is used to transpile Java code to JS code. So, you see the problem here: GWT is used because you need JS in browser, not Java. But it's not a problem for Kotlin, because there's Kotlin/JS, obviously. So why can't we bind WebGL calls to Kotlin calls and go Kotlin/JS?
Tho, I'm not really experienced with GDX inner workings, someone from core devs may point where I'm wrong