While I have no opinion on the "holy grail" part, I think them varying massively is the point.
A lot of locks require a bit of finesse as well, like pulling the door towards you or pulling the key out just the right amount, which would be an interesting challenge. Especially if the technique isn't known ahead of time. Given enough time (and frustration), people can generally figure the "finesse" aspect out for a lock.
We actually have notes taped on two of our doors, with instructions of how to get the locks to line up depending on the season. Another door requires a hard shove during the summer, and a slight pull back during the winter. Someday we'll replace that door with a metal door and get it framed nicely. But we've been saying that for 12 years!
So many repliers have seemed to miss the truly hard part i.e. "keyring" it has many keys and the robot needs to see, recognize and juggle the keyring to only push the correct key in the hole. A human can do this so easily with a single hand
