#1 WWE has invested a lot of time and effort in Roman Reigns
Roman Reigns was WWE's primary focal point since Brock Lesnar defeated John Cena for the WWE World Heavyweight Championship at Summerslam 2014. Roman won the 2015 Royal Rumble and was destined to dethrone The Beast in 2015. Reigns also had a win over the fan favorite Daniel Bryan, defeated legendary names in the business such as John Cena, Randy Orton, Triple H, CM Punk and even defeated The Undertaker at WrestleMania. The WWE officials were so focused on Reigns that they forgot to create other credible stars in the meantime.
WWE has invested a lot of time and effort in the Samoan Superstar. If Roman Reigns is to turn heel, all those efforts would go to waste.
Charlotte Flair to return and wrestle a CURRENT CHAMPION?
Perusing all the points above, we can conclude that WWE may not be willing to turn Reigns heel.