[_ck_]

The terminology here is too close to “auto-close tags” which refers to the bug in bbpress where it’s not closing markup automatically (try posting < strong > here without a closing tag and you’ll see)

What you mean is auto-suggest tags (which I wish were called categories but the blogophere does love it’s crazy little terminology).

The features you ask for are way outside the core and would obviously have to be a plugin (but don’t look at me, I disable tags on my forums).