[psquid]

> an example would be displaying the documentation of some method you are autocompleting, something which I have never seen in vim and which I actually believe is impossible

For python at least, having 'preview' as part of your completeopt has it display the docstring of what you're completing. And :h completeopt suggests that's intended behaviour for all types of completion (where it makes sense), too.

[fmoralesc]

Yes, but currently retrieving that info is done synchronously, so it might slow down things. Under neovim's model, this can be done more efficiently.