What I am guessing for WM assuming no Sting, Daniel Bryan, or Batista
Cena vs Taker (US Title)
Brock vs Rock (WWE WHC) (Rock still has a title shot owed to him)
EDIT: Brock wins the title back at RR from Rollins, and then enters the RR and wins the RR as well.
HHH vs Rollins (face turn)
Reigns (heel turn at RR) vs Ambrose
Usos vs New Day (Tag Team Titles)
Kevin Owens vs Sami Zayn (IC Title)
Finn Balor vs Samoa Joe (NXT Title)
Charlotte vs Sasha Banks (Women's Title)
Bayley vs Asuka (NXT Women's Title)
A few criticisms, probably already covered by others:
1) They won't have two women's titles matches.
2) Cena vs. Undertaker is lame
3) No one wants to see the Usos at Wrestlemania, unless it's during the pre-show
4) They'll need to fit in the Wyatts, and at least one of the following: Big Show, Kane, Randy Boreton, Ryback, Rusev, and Caesaro.
Most likely the NXT matches will be featured on a separate, complementary NXT pay-per-view.
Oh, and I don't imagine Rock or Brock will ever hold the WWE title again.