I'm in shock right now. I always hoped this would happen, but I never really believed it would.
Thank you, Blizzard. You just won yourself a purchase and months of subscriptions money that was in doubt until this moment.
Oh, and by the way? I designed this exact system exactly a year ago Saturday.
Update: To add to the debate and discourse, I'd like to call attention back to this post by Rohan:
It puts forward a very plausible model for endgame dungeon tiers that creates an incentive to run two tiers at once. This could be a good solution to the "Blizzard's taking away half my raid IDs!" dilemma presented by the changes. To boil it down: If you clear the current raid tier and still want to raid, you can go back to the hard mode of the previous tier and still get useful gear.