You could do it that way.
I would have thought, though, that typing anything into an autocomplete where there’s no matches (because it’s empty) would invoke the not found element. Your method, while absolutely valid, seems slightly long-winded compared to having the same method on a single autocomplete element. I’m sure there’s lots of people who want to use it for tags, lists etc. that might start from an empty source so being able to handle it without conditional regions, IMHO, makes more sense.
Will this be going into the next release? I got round it by add an append to the input field which looked like a + button and had a click event to open a modal to add a record purely for when there are no results. Your update is much better.