ADSB will only work if ALL AIRCRAFT are fitted with the equipment. While you have your head inside avoiding the Cessna you can see on your ADSB you could run into the para motor, glider etc which isn't equipped. Any device that draws your attention into the cockpit when you are flying in a 'see and be seen ' environment is unsafe. You will never hit the things you see!
It will be mandatory on all flying objects eventually. The technology will become so cheap and small it will be even in hobby drones or paragliders. We're no more than a year or two away from a crash and fatality between a real plane and a joyriding drone. When that happens, we will see big change real quick.