If you remember before the high defensive line came into vogue most South American teams played with a libero, which was where a defender remained detached at the rear as a last line of defence. (see Micheal Owen's goal v Argentina for evidence)
Don't remember teams ever pushing a No' 9 right up against them if I'm being honest and there were very few offsides.
I'd imagine if Wengers proposal ever become law then we'd likely see that role become prominent again because trying to play offsides would quickly become pretty pointless.