This has to be one of the crazier WWE-related facts. Kingston has never been a main event guy, but he's always been a part of WWE television whether it was winning a ton of mid-card titles or being a part of the New Day. As a matter of fact, from a quick Google search, Kingston and Cena have only been on opposite sides once before - Kingston vs Orton vs Cena.
I mainly find it incredible they haven't faced yet when you realize Kingston is probably in the top 5 of longest tenured wrestlers without having really taken a break. Orton and Cena are the only 2 off the top of my head on the male roster that have been in the company longer than Kingston without going completely inactive (ie Triple H).