According to the whois database (confirmed by Blizzplanet too), Blizzard had gone ahead and registered a dozen of domains with Diablo 4.
That’s right! They have had the Diablo 3 domains registered for a while now but I guess they decided that a single sequel just won’t do. So they got diablo4.es , diablo4.it , diablo4.eu , diablo4.fr … you get the idea.
What’s more – Blizzard has also registered Diablo5.fr , Diablo6.fr and flipping Diablo7.fr in October 2007. I really hope they come up with something to post on these domains… as in a Diablo sequel!