WrestleMania XVIII is in the books, and The Rock has defeated John Cena. In a match for the ages, John Cena went one on one with the great one and failed. John Cena doesn't loose cleanly very often, and it certainly seems like there will be a rematch between the two.
However, Vince McMahon and WWE shouldn't immediately announce a rematch for next year's WrestleMania. The circumstances surrounding both wrestlers, as well as the actual match, make it essential that the WWE hold off on the announcement.
With the Rock's clean win over John Cena, clearly the Rock and John Cena have unfinished business. The WWE cannot let its top superstar lose to a part-time performer without severely damaging their product. It is my guess that the Rock vs. John Cena will turn into a best-of-three series with John Cena winning at SummerSlam and the feud culminating at next year's WrestleMania with a John Cena victory. However, the WWE cannot announce these plans, as it would make the storyline much too predictable for a variety of reasons.
At the current time, the Rock is a movie star, first and foremost. He is committed to making movies and cannot devote all of his energy to the WWE. This much was clear during the build to WrestleMania XVIII.
It is imperative that the WWE doesn't announce a planned match as to avoid creating a similar build. Instead, the WWE should utilize the sporadic appearances of the Rock in order to further the feud between him and John Cena. Due to the Rock's limited appearances, John Cena is going to need a new opponent with which to feud, and this feud will be a perfect opportunity for Rocky to interfere on behalf of Cena's opponent.
However, it is essential that these interferences occur at random and without an announced match, or else they would be much too obvious. John Cena is the face of the company and he cannot continue to feud with a part-time performer.
Additionally, he needs to be involved in the championship picture as well. An announced rematch with the Rock would severely limit the options that the WWE creative team would have in crafting storylines for John Cena during the upcoming year.
By announcing the main event for WrestleMania XVIII a year in advance, the WWE actually placed WrestleMania in danger of being derailed by injury. Injuries are a byproduct of the physical nature of the wrestling world, and the WWE was lucky that neither John Cena nor the Rock suffered an injury that could have forced them to miss WrestleMania XVIII. While the WWE lucked out this year, they need to protect themselves and WrestleMania from a potential injury. By withholding an announcement until a time closer to WrestleMania, WWE will be better able to protect themselves.
An announced rematch at WrestleMania XVIIII also limits the marketing and match possibilities for the event. An announced John Cena vs. the Rock rematch would certainly take top billing, and it would push more deserving matches down the card.
It is a definite possibility that next year's WrestleMania could serve as the last match for the Undertaker or Triple H, which would certainly deserve top billing over the rematch. By announcing a rematch this far in advance, the WWE creative team would be limited in crafting storylines for the build to WrestleMania.
A rematch between John Cena and the Rock needs to take place. John Cena needs to win, and win cleanly, in order to re-establish him as the top superstar in the company. However, this match doesn't need to be announced immediately for the WWE to achieve these requirements. By withholding an announcement of a rematch, the WWE allows more freedom to create storylines for John Cena as well as in the buildup and marketing of WrestleMania XVIIII.