I've been doing the same and like it for macro but when trying to track fast free swimming damsels, wrasse, etc the time between focusing with the record or function button and switching to the shutter is too long. I think it would be interesting to transfer the shutter release instead of auto-focus to the record/function button. That way you can use half-press to get approximate focus followed by sliding forward/backward to get critical focus in macro and still use the regular half-press/full-press for the fast swimmers, but I don't think this can be done.
I think you're right. I was actually replying to "divingdoc" who mentioned auto focusing issues in macro.