As a one time self proclaimed King of the classic A-Frame, I will take a stab at this. Hey, the Mahres did it, it must be cool!
I've been interested in this since viewing Ole Furseth back in the day. Some of this has already been well stated, so sorry to repeat.
First, I think alignment is the underlying root. Someone like Furseth who is naturally bow legged would have a difficult time A-framing, even if he tried.
My experience has taught me:
Trying to ski with parallel shins will help, especially to get equal edge angles. It is not a means to an end.
Pulling the inside leg back through the turn will increase power & allow the skis to have a more parallel & tighter arc.
Adding edge only with the outside knee will only increase edge angle to the outside ski, weaken the legs, cause excessive inside ski lead & divergence.
This weakness will usually cause the skier to make an extra large extension movement into the new turn, interrupting the flow of the CoM.
This weak move will also make the skier less able to let the legs cross underneath & laterally away from the center of mass, or as I like to think of it as "getting my feet behind me". This may be what some of you describe as being upside down?
These are only my own observations though through self analysis & experimentation.
In this context I believe that A-faming is mostly a negative thing, although it can still be seen visually if mis-alignment is an issue.
Using the whole leg (ie. femur) in alignment is strong. A-framing is weak.
After seriously working on these moves for the last 5 or 6 seasons, I could still detect a bit of an A-frame at times. This season I finally broke down & got some serious boot alignment done & the A-frame virtually disappeared from day one. More than one of my respected coaches commented before I ever said any thing about my boots. I'm sure it still happens, but the alignment work sure made everything I've been working on a lot easier! I held out for over 20 years thinking I would have to re-learn how to ski. "What a fool am I".
As far as observing WC athletes using an A-frame. I think that once their hips are so far to the inside & the ouside leg is so extended there is nowhere else for the inside leg to go & remain in balance.
Just some of my own humble thoughts on the topic.Now, should I get another 2/10s of a degree on that left boot?