A lot of people posting that the threat of theft or interference will put a halt to drone delivery, but I wonder if that will really be a problem when looking at the the return on investment. A lot of people have said similar things about self service checkouts but industry keeps pushing on.

The cost of drone delivery will shrink dramatically over time (labour and energy being the two big ones) especially if you compare it to equivalent service levels (e.g. same day delivery) so much so that companies would likely easily absorb the costs - if it all works of course.