Granting them a shot at Tag Team titles at Fastlane would be logical based on what we've seen this past week, but WWE should perhaps hold off on their title victory till WM 32.
Right now, I'd have The Usos vs The Dudleyz in a #1 contender's match at Fastlane. The Dudleyz would win, of course, their heel turn would be off to a strong start and from there, they could start the build-up for a Fatal Four-Way match that's gonna take place at WM.
This all depends on how WWE are planning to book Enzo & Cass when they debut. For all we know, we could see 'em debut post-Fastlane and have 'em dethrone The New Day at Mania, but they could also debut post-Mania. If they debut on a post-Mania RAW, then we could perhaps see Enzo & Cass vs The Dudleyz at Extreme Rules.