This is already implemented. I expose the Sublime completions to vim as a completefunc, so you can hit ^X^U to get Sublime completions while Vim is enabled. I’m also going to hopefully remove the insert-mode input interception so Sublime can still show automatic completion/snippet popups, at which point I’ll query Vim for completion data too to make this work both ways.
The caveat is just that sublime won’t auto-suggest completions as you type, not that they don’t work.
Multiple selection should work extremely well when it’s done, but will take a bit of work to get going (I basically need to track selection 100% on Sublime side, and dispatch a different key to vim per selection, kinda… or wait for official neovim support for it).
The “undo” thing isn’t a huge issue right now (you should mostly just use vim undo), and the insert hack idea that will fix suggestion popups should fix undo too.





(the second two I can work around in horrifying ways, like