Gave this a try a few weeks ago (for CLion with Jetbrains Client, IntelliJ for Java might be further of course) and felt it was still quite lacking. Loads of features weren't there yet. Of the top of my head: no way to use my customized keymap, no git blame annotations, fundamental navigation shortcuts missing (jump back, navigate via file structure), no way to attach the debugger to a process, ...
I went back to remote controlling the full-featured IDE via Projector, their earlier approach too remote development. That works extremely well for what it is. Probably the richer Gateway client will catch up in a while, but not quite yet.
I am able to attach to the remote JVM fine. However the roundtrip makes the QoL features like getting object contents a little slow. But it works!
The main issue I've seen is the gateway/target JVM combo gets wedged in some weird state somehow that persists across retarts and I found myself killing idea processes by hand on the remote server. But hey it's Beta! Works pretty excellent considering.
Yeah, that statement prompted me to try Gateway. It felt a bit premature then. The initial setup is a bit more involved with Projector, which may be a good reason to direct new users to the more recent offering.
I went back to remote controlling the full-featured IDE via Projector, their earlier approach too remote development. That works extremely well for what it is. Probably the richer Gateway client will catch up in a while, but not quite yet.