The fact that JavaScript would break on networks that transparently rewrite JavaScript is a feature, not a bug. If hash codes were implemented by all major browsers, those networks which tamper with JavaScript would have to stop doing so pretty damn quickly, or face a lot of angry customers.
As it is, I think customers would already be angry if they knew that their network provider was rewriting code that will be executed on the customer's computer; anything which makes this more obvious can only be good.
As it is, I think customers would already be angry if they knew that their network provider was rewriting code that will be executed on the customer's computer; anything which makes this more obvious can only be good.