Your posts are so complete and thorough that I can't really respond to both at the same time. So I'll try to respond to the questions you mentioned in the first one, and then hopefully I'll remember to come back and talk about your second one. If not, then bumping the thread will work if you want me to respond to the second post.
1. Does this mean that somewhere in the future there will be an epidemy of hight risk, weird symptom meditators in the re-observation stage? The ajahns, rinpoches and roshis might be puzzled, won't they?
I don't know how many people with full blown personality disorders will actually do full insight meditation. I think that as more and more mindfulness-based practices like the Dialectical Behavior Therapy so successful for things like Borderline Personality Disorder become a part of Western psychotherapy, an attitude will develop that you don't need to do Buddhist meditation to get the mindfulness benefits for psychiatric/psychological problems. Whether or not that attitude will be correct will depend upon how effective future mindfulness-based psychotherapies are.
That said, every personality disorder has a corresponding non-pathological personality type. For example, someone with histrionic personality disorder has a huge need for attention and uses emotional displays, charm, sexuality, and position to make other people pay attention. Their speech is vague, but very animated and even captivating. However, someone who has a histrionic personality type demonstrates the adaptive (rather than maladaptive) sides of these traits. They are charming while still genuine, emotionally expressive but not manipulative, and they enjoy attention but do not demand it "or else." However, the underlying factors of emotionality, charisma, and desire for attention are still there, even if manifested in vastly different ways. Maybe a meditator with a healthy personality type that resembles one of the personality disorders will experience some similar inner territory.
2. Are there any people out there having personal experience about the effect of meditation or know about such cases?
I don't know any people with personality disorders that meditate, though I know some people with personality disorders that I sure wish would meditate.
3. How do affected people, especially those falling in the antisocial category, experience meditation and how do meditation triggered changes in experience interact with the disorder? I'm thinking especially about the possible dissolution of the self-other distinction like described e.g. in the "spiritual rollercoaster"-chapter in Jack Kornfields "A Path With Heart" and as I know it from my own experience. Should't this be the maximum possible impulse towards empathy or a non-aversive habit at least?
People with antisocial PD are notoriously resistant to any attempt to change them. I would guess that if someone with APD started to somehow develop empathy and caring, they would probably stop meditating and let the effects die out. Maybe I'm wrong though -- I've never seen any studies. But it seems more likely that in meditation, as in psychotherapy which also deals with the sense of self, the APD individual would simply never develop caring and empathy regardless of how much a "normal" person would develop those qualities in the same circumstances
.
4. How do people of the antisocial category come to meditation at all?
If they do meditate, their only motivation would be personal gain. Perhaps they are after the siddhis in an attempt to be able to control other people, or they want the status associated with being a spiritual teacher. A great book to read is
Saints and Psychopaths. If that link doesn't work for you, let me know. I have the document on my computer and I can upload it somewhere else if you can't use Scribd.
5. What are the possible special difficulties that anybody affected or his environment has to face in the dark night according to empirical evidence?
I've never heard of any empirical evidence about this, and I'll refrain from guesswork and anecdotes since you specifically asked for empirical evidence.
6. Does Dan Ingram think about specializing in psychiatry (for which he seems unusually qualified) or does he prefer his emergency doctor job (ambulances, helicopters, adrenaline...?)?
I'll leave that question for him to answer if he wants to.