I am not so keen on photon transistors, at least not in the short term. I have seen them proposed for decades but progress has been slow at best. Maybe some folks will figure it out and we will make that leap but current progress is not looking great. As for Carbon nano tubes, I'm not too familiar with the applications of this for transistors but it does sound like something that can get us a little further down the road.

All this arm chair speculation. All the people that work on these things would know far better than me. And I mean ALL the people! ;)