I want to add my personal opinion is the breakthrough leading to AI in optimization. An efficient way to minimize some function with respect to its output. Sounds easy right? It's really * hard, but it's the key thing driving everything.
Some of the stuff happening in 2014 strongly hinted towards the idea that we don't really understand how to do optimization (and somehow we still do really powerful things with our shitty understanding). We have powerful neural networks, but without the right optimization algorithm, they are not as powerful as they can be.
Btw, by bad AI, I don't mean The Terminator. That's silly.
I mean an unstoppable superintelligence that if designed incorrectly will consume all useful matter and energy in the Universe in a rate that converges towards the physical maximal possibility.
You've seen pretty bad bugs right, you know like a bug in a critical system that cascades failures in other related systems? Badly designed AI could segfault the whole f**king Universe. Nobody will be around to file the bug report.
It could even start off with the intelligence of a gnat and end up like this quickly. Hollywood's imagination is limited, and they require silly things like weaknesses humans can exploit. You need that happy ending to sell tickets!