Couldn't find a thread with a similar suggestion, so sorry in advance in case it does exist.
So, new buildable structure/tool - a key on a chain. Requires some wood maybe a few metal bars, or steel nuggets (idea is that it isn't available right away for hermits but quite easily available to villages), can only be built on a tile diagonally adjacent to a gate, so it doesn't block two tile path way, on either side, also requires a key to that particular gate, key is consumed upon building.
After it's in place anyone can close the gate while it's opened and any person who is standing on the same side of the gate as the key chain can open it (though both with criminal act if the gate is under claim). Can be destroyed, though not too easily, in which case it drops the gate key.
I think it would provide much more convenient way to operate common gates, like the one to the village wall and to personal palisade until porting to hf is removed. But mostly that would work for the villages - you can leave (and close the gate behind you) without carrying a key - you can come back the same way by asking some of the village mates to open the gate for you (and they don't have to run back for the key), finally it provides some juicy potential drama when the village gates are open to the sieging forces by a sell out.
I think intrigue potential of it can be boosted somehow if there was a better way to handle getting the key out of it (so the sneaky villager can make a duplicate and sell that, before putting it back in).
Anyway, unless i'm missing any exploit that might abuse it into the ground, that seems like a decent enough idea.