On Smackdown for the last few weeks at least every time they talk about the AJ/Nakamura match they say they're going to face in "the main event at WM".
While that could be just noise, I've heard no such claims over on RAW.
I'm thinking the last 4 matches are Cena/UT, then Brock/Roman, then the mixed tag gets the filler between the two championship matches, and finally AJ/Nakamura.
I have no problem with the Universal title match being the main event either though.