Using user terminals was as much of a thought experiment as anything. The graphs in the video show you can do pretty well just using a few well placed groundstations - you can shave another millisecond or three off with higher densities, but it's not a lot. The big advantage of higher densities is really that you can get better spatial reuse - with more possible choices you can use RF uplinks in places where the spectrum would otherwise go unused, whereas you've less freedom to choose if you've fewer groundstations.
Having said that, this kind of wide-area low-latency bounced routing is never going to be used for you or me to watch Netflix. It will be reserved for high paying customers who really really care about latency. For you and me, we'll be dumped into the terestrial network at the nearest possible location that isn't already saturated.
The second generation of satellites should have optical inter-satellite links, and then you would only use ground relays rarely.
Having said that, this kind of wide-area low-latency bounced routing is never going to be used for you or me to watch Netflix. It will be reserved for high paying customers who really really care about latency. For you and me, we'll be dumped into the terestrial network at the nearest possible location that isn't already saturated.
The second generation of satellites should have optical inter-satellite links, and then you would only use ground relays rarely.