No reason for Rock to be a heel but if they're doing the pointless Rock/Cena rematch, then someone needs to be a heel this time, and Rock coming to RAW in a suit and limo "just because he has a few minutes of free time" would be a tremendous character. Rock was never in a position to be a babyface in the Cena program, WWE did everything they could to turn the crowd on him, they used every manipulation trick in the book, from trying to lie about his passion to attack babyface Foley while presenting his opponent as a poor victim who works hard. Rock is on a red carpet, 3-4k in Mexico smiling and signing autographs - Cena is doing Make a Wish charity and saying that he is never at home. Everything was for one reason and that's to get Cena over, which failed miserably because he only got more and more heat which peaked in Miami for WM weekend at WM28 and RAW. They wanted to give you every reason to hate Rock and love Cena which cost them buys for WM. It was really a pitiful process.
Anyway, Rock appearing on RAW like this:
Reality based, saying that he's The GOAT, bigger than wrestling and all the fans and kids in the locker room should be grateful that he even agreed to lower himself and save this place. Money. Can be a GOAT character. Although the crowd is begging to cheer and sing along and he's doing record business everywhere so it's really unnecessary. But with a possibility of Rock/Cena again, this can be awesome.