I think it would complement, not replace. There are missions that nicely fit the capabilities of UAS, there are missions that nicely fit the capability of satellites, and there are in-between missions that could benefit from long-duration aircraft like this. I live in the east side of Washington DC. We regularly have police helos flying overhead. I wonder if this kind of platform could supplement their efforts for things like tracking escaping vehicles when the police call off pursuit (car chases are frowned upon here due to the fact that they're so dangerous).
Cherry picking examples, UAS will always be best for a construction manager looking at the progress of a highrise, and there's no way an atmospheric vehicle would host a world class space telescope. But things like monitoring deforestation could benefit from a vehicle that can take high-res photos day after day without needing a lot of maintenance and then be packed up and shipped to the arctic to estimate sea ice. A single satellite would have trouble performing both missions.
