Blizzard Entertainment is hard at work on a lot of games we already know about: The upcoming World of Warcraft expansion, the third entry in the StarCraft II trilogy, new content for Hearthstone, and presumably more Diablo III content.
Oh, yeah, and there's that matter of whatever the heck Project Titan is. We may be getting a clue, should a recent European trademark filing for "Metal Arms" mean anything.
Of note is the fact that Metal Arms: Glitch in the System, an absoultely fantastic third-person shooter that released in 2003, was published by Vivendi and Sierra Entertainment, entities that were swallowed up by Actvision Blizzard. In the 2007 Activision/Blizzard merger, the Vivendi Games unit became a part of Activision, meaning that it's quite possible that the (at the time) newly created Activision Blizzard publisher could bring forth a sequel to the cult classic Metal Arms.
That was seven years ago, though. Metal Arms: Glitch in the System is nothing but a fond memory by now. Could the naming then be a coincidence? It's likely, but when dealing with Blizzard, nothing is impossible.
Given the nature of trademark filings that occur months before BlizzCon, there's a decent chance that we'll hear more about whatever Metal Arms is at the convention this October. Surely Blizzard has to announce something major, right?
I really, really hope it's a Metal Arms sequel though. That would just be the absolute best.