Any follower past a certain level can dance any style of embrace. She might not necessarily enjoy it as much, but the general follower technique would hold true for all styles.
In the same vein, if a leader is taught the same way, to be accepting rather than close-minded, they can adapt to any style as well. If anything I think THIS should be the standard in AT... a teaching method rather than a body diagram. Just like learning improvisation is better than learning patterns, learning to follow/match a partner and change the embrace depending on the person you are dancing with is superior to learning one way to do the embrace.
I agree that being open minded and learning to adapt to various partners is a good thing (and other stuff you said in the 2nd paragraph). However, I disagree that being "past a certain level" as a follower automatically means being proficient in any embrace... Or perhaps we have a different definition of what level one needs tobe "past".
I consider myself a fairly capable AT follower and yet I find a pronounced V embrace quite difficult. It's not just a case of varying enjoyment.. I actually become awkward and inadequate in a V with my head turned dramatically to my right. It's VERY different from dancing milonguero where "behind me" is at the back of my head.
Yes, basic follower techniques are still in play, but my entire orientation to my partner is different. What my brain considers "back" is now in a different direction from the orientation of my head, and even my body. Dancing with your hips perpendicular to the line of dance is not the same as dancing with your hips at a diagonal to the LOD.
I can't stress enough just how much changes to be oriented to your partner and the LOD at a different angle. It's actually (with my limited experience of BR) even more different to move that way than to be in a BR hold vs a milonguero AT hold, both of which square off to the partner and LOD in a similar relationship. A great deal of follower technique involves maintaining the relationship to the leader. You can become quite good at dancing in one relationship (ie: square) and still have trouble adapting to a completely different relationship (ie: 45 degree angle)
I think it's true to say that most (but probably not ALL) followers "past a certain level" COULD learn (with time investment) to follow in any embrace. But I don't think it's true that being past a certain level means that they automatically have... unless being able to do so is part of your definition of being "past a certain level".