Roughs seas and landing
This is a DARPA project, so they are pushing against the edge of what is possible.
To take-off from a small platform, even in rough seas, is not too difficult - if you use a catapult to get to initial flight speed. Without some sort of launching system, payload and range will limited.
To land on a small platform is rough seas, is hard. Really hard. In fact, it might be easier to build some sort of robotic "catcher" arm to snatch the drone from the air, when close enough.
The special aspect of this project is not the aerodynamics. This is about what you can now do with flight control through small/fast computers and software. Faster-than-human response times, and more complex processing could make feasible now what was not workable in the past.
Whether this will prove practical, even now, is a question.