Battlefield 4 will not take the shooter series into a different era. DICE general manager Karl Magnus Troedsson said at GDC Europe today that BF4 will be set in the present day.
"We still want to stay in this genre, the modern day as it is," said Troedsson (via Joystiq). "We feel this is a place we can be and continue with the series. Battlefield 4 can live in this space and be very successful."
Battlefield 3 was set in the modern era as well. In its campaign, a madman is trying to start a war between the United States and Russia. Players controlled military personnel from both countries trying to stop the plot. The game ended on a quasi-cliffhanger moment so it seems possible that BF4 could be a direct sequel.
There's really no incentive for them to switch time periods. BF3 sold 8 million copies in its first month. The post-launch DLC is selling well, too, with over 1.3 million players signing up for all-in-one pass Battlefield 3 Premium. While the modern era might be well-trodden at this point, there's still an apparent hunger for shooters set in present day.
What other era would've really suited DICE's purposes? Battlefield is about large-scale battles with air, land and sea vehicles so they couldn't really go earlier than the 20th century. The series has already ventured into World War II and the Vietnam War. A Cold War game would have a lot of overlap with the latter. I suppose World War I would work but it's a tougher sell.
A futuristic setting seems plausible but they already did it with Battlefield 2142 back in 2006. Furthermore, the next game in competing series Call of Duty will be set in the future. Rather than trying to imitate its rival, it seems DICE would rather plant its flag on the modern era. With Call of Duty heading into the future, Battlefield 4 has a chance to be the definitive modern-day shooter.
BF4's beta will be held in fall 2013.