Anyone shot a wedding on the D7100 yet?
I'm not in wedding business now. But D7100 will return DX to weddings at solid groung. From my personal experience it would be best wedding/reportage camera ever (with handgrip).
One simply does not bring a fresh new camera to shot a wedding.
D7100 is in hands of people just about a month. That is too short time to learn all quirks. Wedding is all about moments that cannot be reshoot later again due to camera failing to work properly or photographer unfamiliar with camera failure modes. With two cameras, ok, then you can go if the other one is proven and familiar.
I brought my D90 and my fast primes to a wedding few times (never as main photographer though), yet once when I bought new 32GB SD card week before and tried it only for about hundred of photos, it failed after shooting about 2.5GB of photos at wedding (later I found this was repeatable failure that happened at some random point after more than 2GB of card was filled; camera refused to take more photos with CHA error, already taken pictures were ok). I had other cards too, though I had to lent some more from folks to be more free with shooting. So you need to use gear that is proven, and I mean proven in situations that resemble the real thing.
With D7100 I would also worry about moire. Weddings are full of people in suits. Moire is hard to fix in postprocessing of multiple photos with consistency. It could significantly slow you down with postprocessing - and that is a thing that wedding photographers care about. That is not to say other cameras with AA filter are moire free - the filters in current cameras are already quite weak, weaker than required by Nyquist sampling theorem. But cameras with weak AA filter are going to produce moire only on patterns with strong micro-contrast (see here: http://betterfamilyphotos.blogspot.com/2013/03/thats-moire-nikon-d7100-sample-moire.html ), while cameras without AA filter are going to produce it even when micro-contrast is weak so they are less predictable (like here, patterns on feathers are low contrast yet they produce moire: http://photo.net/nikon-camera-forum/00bVRS?unified_p=1 ).
Otherwise D7100 is great camera performance-wise (if you have good lens set) for wedding. Fullframes are better in some ways (nicer viewfinder, subject isolation with zoom lenses), but worse in others like AF points spread.