LSP does do this, but inconsistently. Document versions aren't always sent (e.g. nothing relating to diagnostics uses them).

It's also not enough to send the versions: you need to actually say what to do with them!

Admittedly my proposal to build everything off more powerful state synchronization primitives does raise the bar for getting _something_ working. Ideally you make it so you can progressively support more features, still. But sometimes you do have to choose between "easy at first, then gets progressively harder" vs "hard at first, then stays manageable".

It depends - the client modules for Emacs' `lsp-mode` generally need a fair bit of configuration. Not just how to launch the server, but also often defining a native-compatible way of setting the options. e.g. for Emacs they often get wired up as `defcustom`s.

LSP syntax highlighting supports sending deltas, so it's not true that the whole source gets sent repeatedly.