It will require a number of innovations just to solve the formation flying aspect of the system, not to mention the other challenges (listed and not)... good luck with that.
Right, but they're flying them close on purpose - point is, at first glance it looks feasible and the close formation aspect has enough benefits that it's worth exploring further. For me, it's the first time I saw the idea to exploit constellations for benefit within the system (here, communication between satellites), and not externally (synthetic aperture telescopes/beaming, or just more = lower orbit = cheaper).