Jim,
The key to this now seems to be when the Snapper is established. At this time, the linemen are not locked in until the Snapper is established. So, in your example, if the snapper has already stepped up to the line behind the ball before A6 moved onto the line, then the “2x2” Exceptions had already been established (A2, A3, A4, A5, A7), and Team A will commit a live-ball foul for an illegal formation at the snap, because original exception A7 changed position.
Now, it seems like the potential Snapper could stand back behind the line and wait until all of their players are in their desired positions. Then, when everyone else is where they need to be, he could move forward onto the line at the ball, thus, becoming established as the snapper, which, in turn, establishes the exceptions, and locks in the “2x2” players. Other exceptions outside the “2x2” may change/adjust their positions, but must be on the line, and between the ends, at the snap.
With this, it will be much more difficult for Team A to disguise eligible receivers.