The relation is that instead of driving around looking for parking, they queue up at their new bottleneck: loading and unloading. Nobody in the video needed to park, and yet traffic within that area was still moving slower than 3-4mph. Place this phenomenon on city streets where they won't have space for conveniently designed queuing areas, and cars will stop in the road, blocking anybody who is trying to move by. Downtown traffic during rush hour will be moving at a snails pace.

I'm open to the idea that carpooling might increase, but where will it come from? If it is coming from public transit, that would be a net increase in congestion. If it is coming from cars, it would be a net win...but self-driving cars should make ubers cheaper, not more expensive, and the relationship with supply/demand at lower cost would suggest that people would move away from uber pools and towards uberx. I would imagine that the more flexible ride-matching of uber pool (compared to traditional carpooling) would make it easier to use uberpool than it currently is to carpool, and with the right incentives (congestion charges that are waived for carpooling?), we could probably make it work pretty well. I don't know though, the complexity of the dynamics here makes it pretty hard for me to predict with any confidence.