I really don't think you can use rotation as an excuse to squeeze in yet another attacker. If we didn't sign Silva then yeah I'd get it but there is no way Pep can keep everyone happy if we also get Sanchez. For one Sanchez is incredibly fit and could and would probably demand to play the majority of the games, Aguero won't be happy playing second fiddle, Sane, Jesus and Sterling would need games for their development and the two Silva's are too good to leave out too often. It just doesn't work.
Plus we have a GK, full backs, midfielder and possibly a CB to buy and Sanchez would be an expensive buy. The only possible way I can see it happening is if we sold Aguero but he's staying.