SLOW
The one problem that is not raised often enough is that most unmanned aircraft (UA) fly extremely slowly. So slowly that into wind at height they can often fly backwards. One of the big problems for controllers is large speed discrepancies at the same level the slower UA just cannot fly fast enough to be deconflicted from a faster aircraft. Therefore, the avoidance needs to be by altitude change and even there it can be difficult as the UAs can have very poor vertical performance.
For the same reason speed discrepancies make 'sense and avoid' a little academic when a UA flying at 80kts is sharing the airspace with aircraft flying at 450kts. In many cases the 'sense' part may have already been cracked but the UA still cannot avoid.
It is probable that even in the future when in theory UAs can 'file and fly' they will need to be restricted in where they fly as they will be disruptive to normal speed aircraft. In Class A airspace the controller will have the task of deconfliction simplified if the UAs are somehow corralled. In class G the UA has to solve its own segregation problem the kind of sensing that is being proposed will 'see through' cloud and be able to track tens of targets so (the engineers claim) it could be safer. However, as the UA pilot has no way of knowing if the aircraft is IMC or not it will be difficult for the UA to maintain legal VFR so there could be problems with unsensed conflicting traffic not being able to see the UAs.