My guess is that first prototypes will be in the market more like 2020 rather than 2017, given that things take time, and schedules nearly always slip, but there seems to be a legitimacy in the air now for BLP more so than at any previous time.
I would gladly accept 2020. However, I'm a bit more optimistic. Some have mentioned sublimation of the graphite dome leading to carbon deposits on the CPV as a potential show-stopper. Mills claims his supplier has guaranteed zero sublimation in the targeted operating range - we'll find out when Mills manages to run his device "closed". I'm also a bit worried about how the cooling will work and how Mills plans to keep the CPV at around 80 C while the dome (just a few cm away) is at 3000 C. I'm not at all worried about the control assembly or the CPV. That's known technology. However, Mills is talking about "recycling" light to increase the efficiency using gold foil on the back of the CPV. That could introduce a new set of variables that need to be worked through.
Overall, I think the remaining challenges are all quite manageable. I was very much of a different opinion when he was rolling aluminum shots through a welder back in 2014. I could see the promise of the technology at that point, but it was pretty easy to see that generation wasn't going to cut it.