The changes added have to do with the rotorwash across the disc as helicopters move. On the video (which you can find above), Austin Meyer, the CEO of Laminar Research explains the concept as well as a bit of the calculations included.
Austin decided not to release 11.40 beta as a general beta because of all the changes added, which can break a lot of stuff in your sim.
You can ask to be added to this beta here. Please note that there is a limited amount of slots available.