Goes with my initial guess that no one in authority has answered because no one outside Dish or even Inside knows.
I swear I will not post here again until Dish reveals the official word. Cross my heart.
I'd say your "initial guess" is wrong. Why do you think Dish owes you an answer now, when the Hopper isn't available yet, and official pricing hasn't been released yet? Could be initial installations will only be new ones, with no mixed receivers, but we don't know, doesn't mean Dish does not know. I think the answer you got was pretty much right on the mark. It is technically possible from all accounts, it's more a matter of what the policy will be when it first comes out. Many policies of new items from any company change as time goes on.