So I do use a tiling window manager, but the problem is that to take advantage of it, I'd need the editor to put each buffer in its own (real xorg) window. I couldn't get something working with either vscode or IntelliJ.

One editor that does support it, is kakoune. I forgot about it when writing my previous comment. Each instance can connect to a server, so they can all share registers/buffers/etc. Then you can use tmux or your window manager to create the layout you want.

It's very clever, I actually think it's superior to vim, as you aren't limited to organizing your views inside a single vim "main" window. You could do stuff like kak | browser | kak, and both kak instances share everything.

Unfortunately I can't get used to the kak commands so I'll probably never change. Perhaps neovim will one day implement something similar.