The Shield reunites (RAW)
If recent rumors are to be believed then Lesnar is going to sign a new contract and WWE might either keep the title on him or have Braun Strowman cash in and win his first belt. Either way, if Roman Reigns ends up out of the title picture then the Shield brethren reuniting would be the next best thing to happen. After all, it was in the middle of such a reunion that Ambrose got injured. The WWE universe is finally starting to sort of accept Reigns as the main eventer. This reunion would complete that acceptance.
A feud with Rusev (SmackDown)
Another wrestler with immense talents who is being underutilized now, he could have a great program with Ambrose. With the split between Rusev and English imminent and probably it would cause some problems with Lana, Rusev can become like a mentally deranged man who picks up a fight with the already lunatic Ambrose and the two could literally tear the house down. Ambrose has already proven that he can hang in the ring with some of the bigger men and Rusev fits that bill perfectly.