Interesting prediction, but I think you're over-estimating the effectiveness of "an average observer." Unless you mean "someone who explicitly is looking for such things" when you say "observer." I go days or weeks without noticing planes in the sky; am I significantly below average as an observer, are drones in cities going to be much more common than planes here, or are drones much more noticeable than planes by 2017? I think one of those would have to be true for this to happen, and I would find any of them surprising.
By average observer, I exclude people actively looking for drones (or other things) in the sky, and I exclude people with training (police? military? spies?) on drone-spotting.
I have been very wrong before! See you (and some drones) in a year!
Try to predict something important in a way, that it will be easy to judge it in 2014, how (in)accurate your predictions really were. Don't leave too much space for a doubt what was really said.