William,
Yes, that was my first thoughts as well. What you suggest is well within our technology, and with the quantity of drones out there it would be affordable especially if it was mandated at some future date.
The FAA also consider this, but rejected the idea. The quantity of drones they envision would overwhelm traffic displays with targets that are of no concern. For the most part anything within 400' of the ground is not a concern to manned traffic, unless we are landing or taking off. (It is more of a concern for helicopters.)
Where the technology seems to be going is "sense and avoid". This requires drones to sense other drone and manned aircraft and then automiously take action to avoid the other aircraft. Now, we are truly talking about the leading edge of our technology, far beyond ADS-B out.
I think the pony would be a lot easier.