The Rock was apparently in talks to come back and face JBL for the title at Wrestlemania 21, and defeat JBL, only to lose the title again on Smackdown several days later. This is apparently no longer in the plans, because the switch was viewed as watering down the title, and the Rock is no longer in the picture for that scenario.
The plan was originally to have John Cena face JBL and win the title, and then have Cena and Randy Orton (who would have won the Raw title) switch shows.
Now it appears that the plan to have Orton win and jump to Smackdown is uncertain, and the outcome of the Royal Rumble on Sunday will give more clues as to where these matches are headed.
credit: Dave Meltzer, Wrestling Observer Newsletter