This has been a very interesting discussion!
I would like to throw out a couple of more thoughts, just to see what the Supreme Court Justices think
First of all, does it make any difference to the discussion that A1 is LEGALLY out of bounds? The arguments stating that the ball is OOB because it is touching A1 seem to imply the usual state of affairs--a violation because the ball is touching A1 who is ILLEGALLY out of bounds. But this is not the case. Would he not still be LEGALLY OOB until the throw in ends? In the case of handing the ball into A2, the violation is not because it is touching A1 OOB, rather it is a failure to pass the ball inbounds.
Second, the rules cited to define when a ball/player is OOB are all framed from the point of view of play occurring inbounds. In such a case it is essential to define when an OOB condition occurs. However, in a throw in situation, play is occurring OOB and it becomes necessary to define when an inbounds condition occurs. Thus a thrower, who is OOB, violates when he puts one foot on the floor inbounds. It is the mirror image of a player inbounds becoming OOB by placing one foot OOB.
Perhaps there are hundreds of holes in these two ideas, but I wanted to know what you think.