Rewrite CustomerContext to a service with interface

I would be happy to see the CustomerContext class turned into a class with an interface, and no usage of the CustomerContext.Current singleton. This way it can be overwritten or intercepted for customization.

In the same way, the logic of Mediachase.Commerce.Security.PrincipalExtensions.GetCustomerContact(IPrincipal), could maybe be moved to the new CustomerContext class so it too can be overwritten or intercepted.

If these were rewritten, then I could make necessary customizations to the customer system and have Optimizely use them automatically.

One example could be this:

Suppose I have a multi-store solution, where one email address can have a CustomerContact in each store. For this to be picked up, I would need to add new logic to CustomerContext and replace the GetContactId extension method logic.