A Grey's wedding to celebrate the 100th episode

Not that I like posting twice in a row about Grey's Anatomy, but TvGuide.com has this news about a wedding during the May 7 episode, which also happens to be the show's 100th. Here is exactly what series creator Shonda Rhimes said:

"The only thing I'll tell you about the 100th [episode] is that it takes place on Meredith and Derek's wedding day."

Well the TvGuide.com post goes on to talk about how unlikely it seems that Derek and Meredith would be rushing to get married after only getting engaged this week. They also speculate that maybe it is someone else who gets married. Here is my thoughts on this. Who else on the show would need to rush to get married? Izzy and Alex. If Izzy is dying, maybe Alex steps up and proposes they get married quickly. But Rhimes did say Meredith and Derek's wedding day, so why do we have to jump to the conclusion that they won't actually get married? Maybe, for once, they will actually lived happily and no drama will ruin their special day.

What do you think? Is a six week engagement out of character for Meredith and Derek? Do you think it could be someone else who walks down the aisle?