So with Coderus' Qt5Websockets packages from Openrepos, it's possible to build Rockpool with the JS websockets stuff turned back on. I've got it running on my phone - the code is in a new branch on github. I don't know of an app to test it with though.

If it works without problems, maybe we could ask for it to be added to the Sailfish repos. It kind of qualifies as a backport...