Hi Lars. Yes I love the auto-unlock too. In my case I have set the auto-lock for 12 min and it is enough to go back for something and return.
Going back to your proposition. It will be rely hard to do. The most difficult part is to prevent auto-unlocking the door by mistake when you are at home all the time. this is why we require you to left the zone. Now we focus to improve the auto-unlock for users for who it is still not work perfectly and we release small fixes every two weeks. I near future we will not be able to implement this scenario