Well, yes or no, i think there's a 99% chance it will be Diablo 3 because of the following reasons:
1. Blizzard seeks people who already played Diablo 1 AND 2 and has a good experience with both games.
2. In the pluses section (I.E: What you get out of participating) is that they say the person will have experience working on an RPG game (Yes, RPG!).
3. One of my friends emailed Blizzard not long ago and they clearly said that they are thinking about a sequel for the Diablo series in the future (be it near or far future).
And as far as second reason goes, it cant be Warcraft RPG because it would be a little bit pointless to have another rpg (World of Warcraft, no need for more), Starcraft RPG would be a possibility, then we got either Diablo 3 or a completely new title. So we got 3 possibilities: Diablo 3, StarCraft RPG, New Title.
But then, first reason eliminates starcraft rpg because its not related to Diablo 1 or 2.
Then again, first reason eliminates chances for a new title because they clearly say Diablo 1 and 2.
Thus there you go, Diablo 3.