This isn't really an answer to your question, but under Gnone3+Wayland "ssh -X" works as you might expect. Which amazed me at first, because I wasn't expecting

This isn't really an answer to your question, but under Gnone3+Wayland "ssh -X" works as you might expect. Which amazed me at first, because I wasn't expecting it. Turns out it's because most applications are X11, Wayland supports X11 applications via XWayland, and X is doing network transparency like it always does.