Although I am not a hardcore researcher of computing, if I were you I would go for quantum computing from your list. I believe, quantum mechanics and computing is a hot topic for research which will lead the classical computing through a remarkable milestone of its kind. Quantum computing is still in its infancy, and I believe that it will only be a matter of few years after which we will see the superfast quantum computers in action in the market. So definitely the HOT TOPIC in computing at the moment. IPV6 is another topic which comes to my mind and I believe lots of things are still needed to be explored in this area. Best, Lonely