Whilst promoting the upcoming Hasbo sequel G.I. Joe: Retaliation, in which he plays Roadblock, Johnson spoke to MTV News about the future of the Fast series.  You can actually watch the entire interview at the bottom of the page, or just skim the text here for the salient bits.

Justin Lin, the director who reinvigorated the franchise with The Fast and the Furious: Tokyo Drift and has been on board ever since, has said that Fast Six will take the action to a new location after devastating the streets of Rio de Janeiro in Fast Five.  Johnson revealed two of the new settings, saying, "We're going to be in the U.K., we're going to be in Germany, from what I know. That's the early talks."

He also added, "And we're going to start shooting in May."

But they won't be shooting Fast Six and Fast Seven back-to-back it seems. “I don’t think we’re going to shoot them back-to-back," he said. "We were going to try that because it wouldn’t make sense to have the same crew and have everybody there in one place, but I think we’re dealing with some weather issues, so from what I know we’re going to shoot Fast 6 first and then worry about Fast 7 a little later.”

Universal Pictures already announced a May 24, 2013 release date for Fast Six, and that would probably be impossible to meet with a massive two-film production, so that could be a part of the decision, as well.

Chris Morgan, who wrote the last three entries in the series, is currently at work on the next screenplay, having been signed up even before Fast Five's release.  Justin Lin is sticking with his flagship franchise despite a flurry of high profile offers in the wake of the last film's huge success.  Vin Diesel and Johnson will once again represent sweaty bald guys who are so ridiculously buff that they can't comfortably relax their arms at their sides.  Paul Walker, Jordana Brewster, Tyrese Gibson, and pretty much the whole Fast Five ensemble are expected to return, along with a character long thought dead (gasp!).