#1 A potential feud between Big E and Kofi Kingston
This is the biggest reason why Big E should turn heel. Not only will that put him directly into the title picture, but the feud itself has the potential to be main event-worthy. When Seth Rollins broke up The Shield, there was a lot of heat between him and Dean Ambrose, which resulted in a very good rivalry between the two.
The same can be possible for Big E and Kofi. There will be some palpable emotion fueling this feud, and that will make it feel sensational. If Big E does turn heel, this would be a proper 'heel vs. face' storyline, which is a rarity these days.
Both Kofi and Big E are hard working athletes; they can engage in a memorable rivalry. This heel turn would be huge if it happens and the match between Kofi and Big E could be one of the biggest storylines leading into WrestleMania.