And why is what I suggested illegal? Which rule "as written" are we violating by shifting the two wide outs into the backfield if we have all ten players with eligible numbers and there is only 2 players in the backfield prior to the shift?
And which rule would we be violating if we had 11 eligible numbers in the huddle, with 86 still in from the last play, and with 4 in the backfield 86 heads out toward the wide out position he simply keeps going off to his bench just prior to the snap leaving "tackle" #23 on the end of the line? And that just after the U and the R have confirmed to each other that we have 11 team A players.
Let's take an extreme example, as you suggest. Team A has the following 11 players on the field: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 and 11. They line up so that players 1-7 are on the line and 8-11 in the backfield with #11 being 10 yards behind the snapper #4 who has touched the ball. Now, if player #1 or #7 moves away from his position at the end of the line (either to backfield or into the team area) and none of the players 8-10 replace him, team A will commit an illegal formation foul at the snap.
If you mean a situation where in the above example #1 never becomes a lineman (continues from the huddle into his team area) the I really don't see what disadvantage team B suffers. They see that team A plays with 10 and see that #2 is the end with an eligible number, thus he needs to be considered a legal receiver. If team A rushes to the line and snaps one second after #1 has gone off the field I think you have a simulated substitution intended to deceive, which is a foul as per 9-2-2-b.