We experimented with X forwarding, but it worked well only on e.g. local networks. Some people still ended up using X forwarding, but JB Gateway or VSC Remote is in a different league.

We have also tried Jetbrains Projector, which is basically a different rendering engine for Java Swing. A remote IDEA instance was rendering the UI through HTML, i.e. you could develop in a browser. It worked relatively well, but there were some issues around copy/paste, etc.