I am very glad to hear that tag autocompletion is on your story board.
It would be great to not only consider the beginning of the entire tag path for autocompletion but the individual levels as well. What does this mean? Well, lets say I got a lot of tags related to individuals summarized unter #person/..., e.g. #person/felix. It would be great to get the autocompletion suggestion "#person/felix" when I just type "#f" instead of typing "#person/f".
I feel you have an opportunity to steel Evernote users at the moment because their latest iso update is painfully slow. Really want to migrate to you but tag autocompletion is an essential feature otherwise i end up misspelling and creating new tags instead of tagging with an existing tag