Drones are one of those cases where I think it is a matter of "the devil is in the details".
Yes, there are times when a drone would be an ideal security platform: a bright sunny day, low/no winds, open area, away from airports, no concern of the noise of the drone giving away its position or altering those being monitored.
Most security applications are not that ideal scenario though. You have windy conditions, a desire to be somewhat covert, low light and so forth. I think if someone is investing in a drone for security, given the amount of money being spent they would want something close to 99% availability. Even assuming the drone would be allowed to fly at night, I think you would be lucky to get above 50% total availability/usability after you account for charging time (or even returning to base to swap batteries out) and weather.
Another issue I see with drones is height/distance/angle. We can usually mount security cameras as low as 15' high and still consider them secure from most vandalism threats. A drone would most likely need to fly much higher to ensure it can't be easily knocked down by a thrown rock or similar. This increased height would affect viewing angle or distance to target, needing larger lenses for the camera onboard, or you'd have direct overhead shots that could obscure details of a persons face.
At a base level, controlling a drone from a VMS isn't that difficult, but I think that these "proof of concept" demos are a very long ways from a product that could be widely commercialized. The FAA regulations are inhibiting investment in this area, IMO, and I think there is a lot more R&D that would still need to be done.
If the FAA dropped all drone regulations tomorrow, I think we're still 2+ years from something like "drone as PTZ alternative".
In the US, every air incident is investigated by the NTSB and FAA to determine root cause.
Based on the findings, 'responsibility' is determined. I'd expect that for drones, the same sort of plan would be built out in the US, especially since flying drones already has the precedent for being a restricted activity.
Btw, this company, Cyphy is offering a tethered drone, which they say would eliminate the legal issue as well as eliminate battery and wireless limits (of course it adds a wire in the air). They are also using an Oncam panoramic with it. We have queued up to do a post on this.
The FAA is supposedly releasing some updated drone regulations this week. The speculation is that drones up to 50lb will be able to be used commercially at low altitudes. However, still only during daylight, and still requiring them to be in sight of the operator.