Blizzard's effort to keep Diablo 2 playable on modern PCs and operating systems is laudable, but it may also be somewhat less essential than it initially appeared: A fellow by the name of egod123 is recreating Diablo 2 in StarCraft 2, and a new trailer heralding the upcoming alpha release is looking very nice indeed.
The Curse of Tristram: Destruction's End is actually a mod for StarCraft 2, and so while it will be free, it will require that game in order function. Egod123 said on his Patreon page that most of the “core systems and functionality” have already been completed, and egod123 is confident he'll be able to complete work on the project with some support from backers.
Of course, that doesn't address the risk of a cease-and-desist letter from Blizzard, which would stop the whole thing in its tracks. The fact that it's a homage of sorts may lessen that likelihood somewhat, especially in light of the studio's relatively forgiving attitude toward fan-created content: The StarCraft Universe MMO is still drawing breath, for instance, and you can play the original StarCraft and Brood War campaigns in StarCraft 2 if you're so inclined.
Of course, there's a much more recent example of a much less happy ending to an unofficial Blizzard project: Just last week, the studio took action to close down Nostalrius, the largest private Vanilla WoW server in operation. But that situation was also quite a bit different in that Nostalrius could be seen as cannibalizing World of Warcraft, Blizzard's number-one cash cow. I don't think anyone is going to seriously suggest that Diablo 2 sales are going to suffer because of this mod, especially since it's dependent upon ownership of another Blizzard game.
Absent of a letter of permission autographed by Mike Morhaime, I'm hopeful that The Curse of Tristram will continue development without inference from Diablo's owners. Even in this relatively early state, it looks fantastic. The Curse of Tristram is set to begin alpha testing this summer. Follow along on Facebook.