There should be no illegal formations. Then we can play without as ST thus using the new tactic of False 9 which has shown gr8 success. Also, I would love to play without players on the flanks.
No illegal formation means we can even 'Park the Bus'. Then as someone had mentioned in some thread, we can use the W/M style. So many more options will come if there r no illegal formations thus making the game more real and versatile. After all, being a better manager includes experimenting to make new and better formations and tactics!!!