Meanwhile I'm checking Helix editor every 6 month to see if authors became any less hostile to the idea of thinking about considering of starting thinking about potentially adding copilot support. https://github.com/helix-editor/helix/discussions/4037
Helix is working on a plugin system that will hopefully allow for copilot (or whatever other product) use. Also, the Helix way, thus far, has been to build a LSP for all the things, so I guess you'd make a copilot LSP (I be there already is one).
I don't know the LSP spec well enough to know if these sort of complex interactions would work with it, but it seems super out of scope for it imo.