To me, seems pretty obvious that they set up Fast Lane for 2 reasons:
1) To try to get Bryan & Reigns over as friends to at least some of the YES chanters
2) More importantly, to set up a chance for someone to interfere in their Fast Lane match and cost Bryan the match in an attempt to transfer the heat on Reigns to this person interfering (presumably Sheamus, but never put it past McMahon to make it be Big Show or Kane b/c Vince knows that deep down we all want to see more Kane & Big Show angles). The goal is obviously to get people to blame the guy interfering for keeping Bryan out of Mania & get the boos off Reigns (hence the reason for Step 1 above) so they can keep him babyface & let him stay on track for becoming Cena v2.0, but I hold out little to no hope that it works like they hope it will. I foresee there being more than enough boos & jeers to go around
The irony of the entire situation is so beyond the pale, though, that one cannot help but appreciate it. Daniel Bryan gets over with the casual fan due to being an underdog (& with the more hardcore fans due to his in-ring talent), yet WWE continues to buck against him, keeping him over as the underdog in everyone's eyes. Meanwhile, they try their damnedest to book Cena & Reigns in 1-man-against-the-world roles to get them over as underdogs but nobody over the age of 8 buys it and those guys get booed relentlessly not only by the hardcore fans but increasingly more by the casual fan. If they'd just go back to basics on a lot of their booking then they'd be far more successful at getting over the 2-3 guys they actually want to get over while still being able to keep over the fans' own favorites like Bryan (& Punk when he was there)