I'm not sure removing the rule would induce goal hanging at the top level. Teams defend with 11 men, and managers wouldn't plant a centre half in the 18 yard box because they would be a passenger for most of the game. Instead I think the changes to the game would be more subtle, pacey players lying a foot goal side of the defender, waiting for the ball over the top.
Defenders couldn't play such a high line and as a result would play deeper, and that would create more space around the pitch. I've actually thought about this in the past and thought it would be quite a good idea, although with it being such a fundamental change I don't think it will go down well with fans.
The best thing about it is that it will eliminate any offside errors which we often see have a huge baring on a result.