The spectrum is going to be so crowded by the time this is in full force.. Then what would they do?
Also, on top of that, an open network with no encryption? It seems like that would be a great place to do some MITM attacks, as well as a variety of other things
AFAICT, that's just for the public access points, though, yes?
Well, there's 10 GHz of available in this band (71-76 GHz and 81-86 GHz) and full-rate gigabit can be achieved typically with 750-1500 MHz of spectrum (depending on vendor and, mostly, modulation).
In addition, this spectrum requires a license (as low as $75, IIRC) and they are pretty easy to get in this band ("lightweight licensing").
80GHz doesn't leak in every direction the way 5GHz does. The antennas have 9 channels (each 500MHz wide). Also, you can reuse the 9 channels by using a horizontal polarity instead of a vertical polarity.
Looks like a shared gigabit system. How does this scale?
These are point-to-point links so it's not "shared" bandwidth as with, for example, cable modems. It will be dedicated links between the endpoints.