#1 An eventual heel turn for Lashley or Reigns

Bobby Lashley and Roman Reigns had a rivalry this past summer that culminated in Lashley winning their one on one match at Extreme Rules, after which The Big Dog got his win back on an episode of Raw.
Lashley and Reigns haven’t interacted much on air since, but if WWE were to put them directly in each other’s line of sight again, one has to believe the old tensions would eventually pick up again. The two have already worked a face vs. face feud—a mold WWE typically steers away from, and a set up WWE likely views as played out at this point. No, when the time comes for WWE to revisit Lashley vs. Reigns, it will probably be with one man as a heel, and especially so if it comes out of them working together under The Shield banner, and then splitting up.
Lashley would be the more obvious choice to go rogue, given WWE’s seeming commitment to keeping Reigns face and given Lashley hasn’t worked heel yet with this company. Depending on the timing and surrounding circumstances, though, things could conceivably break either way.