Barrett, with his new Nexus, and a few new additions who are jealous of Taker, and want to take him out permanently, get into a feud with Taker upon his return(This is assuming that Taker doesn't finish up his feud with Kane by dominating him, and then putting him out of action for several months to make it look like Kanes gone).
One Smackdown, Taker is cutting a promo, or in the ring after a match, and Nexus show up. They surround the ring on the apron, get in the ring, and then each of them hit Taker with their finishers. Then Barrett goes on to say that he had a plan all along..that he has kept secret for when the time is right. And now he reveals that he wants to end the Undertaker's WM streak, so that he can be the phenom of the WWE, and be the one talked about instead of the Undertaker.
Next week, Taker is in the ring, cutting a promo on last week's attack, the streak, and Nexus. Nexus show up again, and surround Taker on the ring apron. They are ready to pounce. Kane's music hits and Kane helps Taker scare off the Nexus. He then cuts a promo saying that blood is thicker than water, and that hes not got much time before he retires(but Kane will say something like "Before I rest in peace"), so he will do the honorable thing, and fight alongside his brother to defeat the mortals, like they used to. Taker and Kane will make amends, and do the kneel down/hands raised gesture in the ring, while Kane's pyros hit.
Taker and Kane don't have to wrestle every week, but they can cut legendary promos, to give us a good buildup. When they do wrestle, they can take on members of Nexus in singles matches, and win some, and lose some(due to several other Nexus members interfering). They should make Barrett and the Nexus look tough too, by having them take out Taker or Kane backstage, on the way to the ring, or have them use weapons in matches with Taker/Kane.
This will make it seem that Barrett and Nexus have a big chance to beat Taker and Kane at WM.
There you go, this sets up for WM: The Brothers of Destruction vs The Nexus.