FWIW, Dan has a video on that issue here. Possible, but far off, he says - citing software issues:

http://bigthink.com/ideas/daniel-dennett-discusses-the-problem-of-robotic-warfare

How hard the software will be is an issue to which currently nobody really knows the answer at the moment - AFAICS. We might all have our gut feelings - but I think nobody who is trying to be rational really knows - or even has a particularly low level of uncertainty just now.

Commodity hardware won't get there until at least 2017 - and software lags behind hardware - so probably some time after that we will have affordable machines that can do a lot of what our brains can - but how much after that... my assessment is that nobody really knows.