I just looked at a video from a flight earlier today and noticed something that has never happened to me before -- I encountered another drone in flight. There was another quad (from the shape and color it could have been a Mavic, Mavic Pro or possibly a Mavic Air in black) about fifty feet below mine on almost a reciprocal heading.
Very cool. It looks like it was flying really low. Unless I was on top of one of those buildings, I would be afraid of losing signal in an urban place like that.
It happen to me once while flying in Hawaii, I was capturing the sunset when
a Mavic Air flew in front of me about 10ft away and we were about the same height.
Be careful what you wish for, ads-b out may reveal more than you want... the whole remote ID thing is coming like it or not. However it would be cool to know if some other drone was getting close.