Well, I'm not a fan of GURPS so I would say its a contender. However, I doubt that it will ever get huge. It will probably get about as big as Deadlands once was. I think its more on par with the size of the fan base for BESM.
The light, nearly transparent system of Savage Worlds isn't going to go over well with everyone. It paints with very broad strokes that allow for a very cinematic game but at the cost of detail. I don't think you're going to find a better system for fast play of huge fights.
Evernight, when its released, is said to be kind of revolutionary. I think its a bit of a heady claim, but they are doing some thing different. It's set to be a setting/epic campaign all in one book. It stems from the author's failed 2nd ed D&D campaign where the heroes failed to stop the illithids from blocking out the sun. Hence, evernight. It's a string of scenarios that they claim that the DM can pick up and run in minutes! No work. It also takes the PCs from Novice rank to Legendary rank so its pretty epic. Plus, though the actual campaign is pretty linear, there is a lot of side quests and room for player initiative. So it all claims. We'll see when it's released.
Not to sound like an advertisement, but Pinnacle has a bunch of free stuff for download on their site: The Test Drive Rules, a fantasy adventure, a Cthulu-esque adventure, and a pulp adventure. A pretty big taste of the game. The design diaries are also well worth reading.
http://www.deadlands.comHeh, maybe I could get a job pimping out Pinnacle...