This tech is really cool, but as they mentioned, they have not tested this with a moving satellite. Because any antenna would need to be localized on a satellite for transmission, you’re going to be stuck with having to maintain (likely) expensive and precise motors who’s job it will be to run in perpetuity. However, I would be confident that stepper motors of this grade will come down in price or will become more available.
My primary concern comes down to reliably. Your ground station must now accurately target moving satellites, negotiate handoffs, and reroute when necessary. Architecturally, you will need to develop the ground station with at least three transponders: an A link, B link, and a redundant Z link. The A and B take turns localizing to their satellite where one is only allowed to move positions if the other is currently active. The backup Z link is on standby in case of failure or maintenance. The three would likely rotate roles periodically to keep time on each of the motors more evenly distributed amongst them. This system must work in harmony with all the satellites in its network. The satellite system has its own maintenance burden too, including orbital decay requiring you to periodically adjust its position until it runs out of propellant, and send more up when it’s reached the end of its useful life. To me, this is a ton of moving parts.
An undersea cable by contrast, will pretty much be maintenance free once laid only requiring infrequent repairs in the event of a wayward ship anchor. Yes, the data center components will need to upgraded periodically but you don’t need to replace the transmission mode. There are no moving parts, no need To track objects hundreds of miles away, just sending light down a tube.
Is this tech cool? Absolutely. Will it replace undersea cables? Probably not soon, but I can see this as a great solution to link remote islands where it does not make strategic sense to run a cable, or where it is difficult or uneconomical to run a terrestrial connection.