But I am also sympathetic to the concern that talking about difficult stages will cause a knee-jerk reaction against all meditation.
This is a good point and I think it's pointing to a big part of the problem, most people think, due to years of pop-psychology and self-help bullshit, that meditation is all fun and games, that by sitting on a cushion for 10 minutes a day you're life will be transformed in wonderful ways when, as you and every single person here knows, it's so far from the truth.
I really hope that, however long it takes, this research and your entire project will help lead to a clearer understanding of this as it's something which needs to be examined. The spiritual crisis is inherent in every tradition from Buddhism to Christian mysticism so the lack of honest, straightforward discussion on the matter, not dressed up in metaphor and esoteric symbolism, is baffling!
If I come across any other teachers or high-level practitioners willing to talk about this then I'll drop you a message.