With the scenario of catapulting someone new into the main event to win their first world title, it has to be someone that not only is over with the crowd enough to convince them to buy the ppv, but also over enough with the audience as someone who could actually win it. As KB pointed out, if Dolph Ziggler suddenly won the Royal Rumble and then the WWE/WHC title at WrestleMania, there would be a backlash of people saying that he wasn't ready and that they just did a hotshot to him, putting too much too fast onto him and overlooking other people that are "more qualified". I like Ziggler, but he might even be too green for a MIDCARD title reign (though most likely not), let alone the top position in the company.
Now, Sly pointed out another thing that I agree with: being worthy. Am I tired of seeing the same group of people in the same positions? Yes. Am I very glad that Smackdown allows some fresh feuds and it seems to be elevating EVERYBODY on the show, as opposed to still just focusing on 4 people (Orton, HHH, Batista, Cena)? Very, very pleased about that. But when it comes to people that would be ready for such a monumental thing like the Royal Rumble/WrestleMania duet, the list is minuscule. People like MVP, Shelton, Christian, Swagger, Kofi, The Miz, Morrison, Matt Hardy...they're the ones we're primarily thinking about when it comes to the list of potentials, right? I'm a fan of all these guys save for Matt Hardy, and I'd love to see them all be world champion some day (save for Matt Hardy), but there's something that just SCREAMS out to you when you look at this list. I'll give you a second to think. Proceed to the next paragraph when ready....
Money in the Bank. These people are prime for a Money in the Bank win, because they're all upper midcarders, and the MITB is built around the concept of giving an upper midcarder a push towards the main event that doesn't revolve around them needing to sell tickets. I'd love to see John Morrison win the Royal Rumble in 2010 and go on to defeat someone like Chris Jericho for the championship at WrestleMania. Morrison's one of my favorite guys on the roster right now and he has a bright future. But if you really think about it, wouldn't it make much more sense - if its medically possible - for Edge to return as a face, win the Royal Rumble (something he's never done before), and beat Chris Jericho instead? Edge/Jericho will sell more tickets than Morrison/Jericho, plus you have a built in system that allows Morrison to win the Money in the Bank that same night and begin his main event push. Its just delayed by a couple months. This is why Randy Orton won it this year, because he's an established name that helps the credibility of the Royal Rumble and he should have been in the main event without a doubt. I thought HHH/Orton sucked major ass at WrestleMania, but from a logical standpoint, it made sense to have that match. Now that Orton won the Royal Rumble, it adds another big name to the list of people that have won it. If Edge were to win it in 2010, that's another huge name. Then imagine if in 2011, we had Dolph Ziggler, a guy who has been IC champ a few times, has had some upper midcard experience, and so forth, starts a slow build and BAM, he wins the Royal Rumble. Doesn't that mean more when he can relate himself by being surrounded by credible multi-time world champions, as opposed to every year just having a new superstar go ahead and win his first WWE or World Heavyweight title?
The Royal Rumble/WrestleMania push is a great way to get a new main event star for years to come, but because of its very lucrative position, it should be reserved for people that can make the most of the situation, instead of just degrading it to an "emergency push" for someone who needs to move up the ladder.