For the purposes of this argument I went and installed VSCode. I cloned kubernetes/kubernetes, opened a random file, added fmt.Println("hello") at the wrong indentation level somewhere, and pressed save. While gopls is initializing, it pops up a thing saying "waiting for code actions from the language server" (or similar; it wants the language server to "gofmt" the file). After that completes, the line I wrote appears at the right indentation level in the editor, but what's on disk is `fmt.Println("h` at the wrong indentation level.

Emacs behaves in a different but still incorrect way. It writes the entire fmt.Println statement at the wrong indentation level, locks up for a while, and decides that there was no formatting to do. VS Code will be fast after a while, but Emacs never gets fast; every reformat request locks up the UI for several seconds and doesn't actually reformat. VS Code remains responsive, but it's difficult to get the reformatted text on to disk. (Sometimes it does it, though.)

My main conclusion is that you're screwed if you have to work on k8s day to day. But on a more serious note, this isn't really an issue that can be solved with a UX tweak; the class of problem is "the optimal algorithm for providing instant hints on a codebase that is 214k lines hasn't been discovered yet". Yes, editors can let you mutate the text while it's working on something in the background; and if you turn of language server support that's fine. The key problem is merging your edits with its set of assumptions, and that's what's going to be slow.