You really think he'll come back to fight Ryback? I dunno... On one hand, a part of me would like it because it's a part timer working with someone in the midcard (which is what a lot of people have been complaining about not happening with guys like Rock and Lesnar for the most part), but on the other hand, Ryback doesn't have much credibility after being jobbed out to pretty much everyone. They'd have to do a 180 immediately and start booking Ryback as a machine until Mania gets here in order for Ryback to have any cred going up against Goldberg.
That said, I share the opinions of others on different forums that Goldberg/Cena for the WHC would be an interesting encounter. It's a match I could actually see Goldberg agreeing to, and the storyline is there - Goldberg wants to win the WHC one more time and go on one last run. It's the one championship he's won in WWE and it's a championship that is modeled after the same belt he won in his historical match with Hogan back in WCW. Plus, WWE would no doubt love to have Cena go over another legend like Goldberg (assuming Goldberg didn't actually shock people and win the WHC in a big last historical moment... I seriously doubt it would happen, but who knows. If WWE signs Goldberg to a one year deal or something, they could get people believing that it could actually happen.)
This would be a great handful of top matches for Wrestlemania XXX (though I have a few different ideas for what the event could end up looking like):
WWE Championship: Daniel Bryan vs Triple H
World Heavyweight Championship: John Cena vs Bill Goldberg
Undertaker vs Brock Lesnar
CM Punk vs Randy Orton