...Backpacker's suggestion of technical solutions seems entirely feasible. Computer vision systems are advancing at a tremendous pace, and are already far more effective at detecting visual anomalies (albeit with a modest false-positive rate) than humans. Of all the computer vision problems that are being worked on (facial recognition, human behaviour recognition, etc.), spotting an aircraft that's on a collision course is relatively straightforward algorithmically. It's quite plausible that within three years, we'll have UAVs that are better at detecting potential VFR traffic conflicts than pilots. Combine that with TCAS, and UAVs programmed to take deconfliction action with some knowledge of the other traffic's likely behaviour (e.g. observing the Rules of the Air), and I don't see how they'll be a significant increase on the mid-air collision hazard as it is right now.
michaelthewannabe, yes, I see the options, a simple google search shows the effort being put into UAV vision and aviodance systems.
The mid-air accidents/incidents in Iraq best show the
current situation of how an airspace saturated with UAVs and manned air vehicles will operate.
While improved UAV aviodence systems may be under development, theres no guarentee of succes. For any current airspace discusion, I would think it
prudent to only use the currently demonstraited
dangers of large numbers of UAVs operating with manned air vehicles.