I suppose the ViP612 could be considered the upgrade. I don't think there will be any more non HD boxes released by Dish. Gotta be cheaper to make 'em all HD and just turn on the feature when subscribed to. They'll have to change their current list of charges, though.
When? Don't know. It's been talked about for quite a while though, so it may not be much longer. I tried to search for it, but the search function on the site is, err, "limited."
Do you have a 625 or are you considering one? Unless you want HD, there's not much point in getting a ViP612 or ViP622.