According to PWI, WWE is currently considering Styles vs Taker for the WWE title at Royal Rumble next year.
https://www.reddit.com/r/SquaredCirc...ible/?sort=new (Original post ended up misreading the event rumored thinking it was at Mania for Styles-Taker).
Might be a way for WWE to do Cena-Taker and maybe Cena's 16th reign if they were to go that route for Mania. Or maybe Orton-Taker for the WWE title if Taker were to win at the Rumble and WWE keeps that match as the plan for Mania.