I kind of lean towards double the schedule and cut the scope in half and hope that maybe we can deliver a little extra credit work.
It's important to note that padding schedules is not just done in software, it's a common practices in all sorts of engineering. It's not bad that we do this, it's bad that management often doesn't understand that we do this and doesn't understand why. The understanding why part is actually really important, because that means management can be expected to do their part in managing the uncertainty or at the very least they can be expected to be careful about not making the situation worse.