Distractions are an important point.
Ideally, if everyone has ADS-B you would see, during your scan that there is someone ahead, similar altitude and heading your way. So you take some avoiding action and try and get visual.
What actually happens at the moment is, there isn't a mandatory requirement in EASA land so not everyone has the device and there is a lot of complacence around that - just because YOU have ADS-B in Class G doesn't mean everyone else does and doesn't mean the magic tablet is gonna always get you out of a sticky situation. So, we end up with more heads down in the cockpit. The other problem is what happens if everyone has ADS-B? Well, in some areas you're going to end up with a big yellow blob on your screen - fat lot of good for anyone! As the Dutch found out at Schipol when they made Mode S mandatory, more isn't always better in the context of radar clutter
Drones? There needs to be some kind of proper certification for them and training. I don't like to be a spoilsport but it is stating to get silly the no. of drone related airprox. All it's going to take is for one to get ingested, then the large lithium "bomb" will go bang and you'll have an engine failure/fire/dismembering of turbine.