I am surely not getting some part of this, but it seems to me that the paper and the video (both listed on the official Lightning website) contradict each other. In particular, the paper describes a simple bi-directional payment channel in Section 3 using only one timelock value (1000 blocks). In the video though they claim that in order to reverse the direction of the channel you have to use a shorter timelock (which makes indefinite number of channel updates impossible).

Are decrementing timelocks actually used in simple bi-directional channels? If so, what would go wrong if new commitment transactions were just created with the same timelock value, say, 1000 blocks?