I’m also not qOS nor do I have as much experience with subs as someone like Jouissance but I want to weigh in a bit because the INTP point is something I’ve actually been thinking about recently.
Long Post
I’m an INTP myself and quite a bit older than your friend. In the past, like 5+ years ago, I’d actually read most of what Jung wrote on personality types, a few academic texts on it (there’s a book specifically on INTPs by Dr. A.J. Drenth that I remember being pretty good; he’s also an INTP himself), but I hadn’t really paid it any mind for a while.
But I was just thinking the other day: “you know, a lot of my work on subs (and in general) has revolved around dealing with common INTP weaknesses”.
This is stuff like overthinking, disinterest in mundane tasks/conversations, aversion to too much structure/routine, etc.
However, the most disruptive thing for INTPs is their “inferior” function, Extraverted Feeling.
For people who aren’t aware, your inferior function is “weak”, in the sense that it’s underdeveloped, but it’s actually a core part of who you are and has a very strong emotional charge, both positive and negative.
https://personalityjunkie.com/02/introverted-thinking-ti-extraverted-feeling-fe-intps-entps-istps-estps/
So, I could be wrong, but I wouldn’t be surprised if your friend relates to something like: there’s a part of him that cares less about what other people think (hence being willing to be outwardly eccentric) but there’s another part of him that REALLY cares about what other people think. As well as a part that is kind of emotionally detached from other people but another part that REALLY wants deep emotional connection. They may understand emotions but not know how to express or manage them smoothly.
With that in mind, I think WDB could be great. But it’s a little more external, as far as I understand.
E.g., Saint/qOS suggest combining WDB with Symphony (Heartsong Stage 2), as well as running Attuned (HS St 1) before WDB.
This is relevant, because I personally feel like new HS may be THE foundational relationship title for INTPs. With Attuned actually digging deep on the Extraverted Feeling issues and Symphony helping express them.
I think Reforged is also very relevant here as not only does the copy address the ability to express oneself romantically without viewing it as a judgement on their self worth, but this is my first cycle with it – and it makes me VERY aware of all the ways I’m mentally fixating on what other people thing. And interestingly, lately I’ve started to notice when other people (through their body language, etc.) seem to be worried about what I or others are thinking about them.
Plus, as I think a lot of us know, modern dating can be brutal for young men, especially if they’re inexperienced and/or interested in more serious relationships. Hence the more foundational, masculine, frame-holding title as a backbone.
In short, I’d be really curious how Reforged + Attuned works for them, then moving on to WDB/Symphony, etc. later. Partially because that’s possibly my next stack 
I’d add that, even though this stack is more “internal”, at least until Reforged starts pushing outwards, INTPs don’t tend to care about being social butterflies and you say he doesn’t actually have problems socializing. So, just feeling more comfortable in his emotions could have already external effects. Their feeling function is already outward facing, by nature.
But again, qOS could completely disagree with me.
