Only thing I don't think you can do is take Ryback to Mania as your champ. Mania is their one chance all year to draw casual fans back in and many aren't going to recognize his name.

But Punk is a different story. They easily could've taken him to Mania as the champ and put him against Taker in a "Title vs Streak" match that would've drawn huge. Also, you're right in that there's no reason you couldn't have done another Cena/Rock match without the title.