I understand if Blizzard don't want to host the servers themselves but maybe there is another win-win solution without shutting down private servers, maybe cooperation?
What if Blizzard had a certification for third party providers like Nostalrius? Blizzard would only set up the conditions that must be met with the provider so they can be certified and legally host a server with older version. Everything else would be done by the third party, from writing the source code, development, customer support etc... Obviously the conditions would be very strict to make sure people have the perfect near experience of the game and not everyone makes a server.
Certified servers would need to have a monthly fee, and the revenue would be split between Blizzard and the provider in a certain ratio.
I think this would be the best solution and it almost wouldn't cost Blizzard anything. I think the main reason they don't want to do this themselves is because they can't plan with legacy servers being popular and profitable for the long term. But with this method that wouldn't be an issue.
Thoughts?