Not just Unmanned . .
Of course, the 'answer' will not just apply to Unmanned Aircraft. What's good for UAV's/UAS/RPAS will apply equally to any 'flying machine'.
Once the technology is cheap enough who would not invest in an extra 'box' to help detect/identify other aircraft in close proximity? Maybe even an iPad app?
BAE's Jetstream team have previously tested ADSB and IR Camera technology as part of a possible solution to aid 'sense and avoid', and that work is continuing (as we speak) under the Astraea 2 programme.