Best case scenario - announcement of a new game set in the Diablo franchise, and a commitment to expansions/patches until it releases.
Worst case scenario - new title, and rehashed seasons in D3 for 3-4 years.
It depends on what they see as the future of the franchise. Blizzard North reputedly only wrote enough story for D3, and nothing past that - and that material was vaue, at best. I've read that they've gone back and forth on what Diabo IS, and wether to have PvP or not, or whta kind of story, linear or non-linear, one version was scrapped by Vivendi, which led to Blizzard North being shut down, and Irvine taking over. They inititally announced that D3 would get several expansions, but backed off that. There's rumors a second expansion was planned, but scrapped. (For those of you bathering that "Blizzard only does on expansion" - D2 was supposed to get a second expansion, but it was scrapped in favor of the doomed D3 version Bliz North worked on.) Jay Wilson said that elements would be added to D3 to eventually go into an MMO, but that was scrapped.
The whole history of the game is disjointed and screams that nobody really knows what the game IS, and what it's going to be in the future. Nobody seems to take ownership of it, and it's identity, it's simply remolded to whoever is working on it at any given time.
So, yeah. This new game they're hiring for means they may have figured it out. What it is? Who knows. I'd love to see a Witcher/GTA/Fallout type game set in the Diablo universe. But it's unlikely. Blizzard is all about Battle.net and eSports, so it could be a dungeon arena type game, for the PvP types.
Two months, we'll know. I just hope part of it is scheduled for 2017, and not 2020.