I understand the ruling. To be fair and honest, there arent many occasions where you don't know you have been hit.
As long as refs are more pro active, it could work. I had a ref watch me at a PA, and saw me get hit on the pack, I didnt feel it, and he pulled me with the Sosta rule. I sort of agreed that I was playing on unwittingly, and got my ass in the dead box. That was fine (ish) until he told me after the game that he waited until I played on to pull me!
lol, he was very polite though, and I dont think he realised what he was saying.
My point is that as long as refs can use some discretion, then it could work a treat.