Agree with this 100%
Like I said before what the OP wants just doesn't exist or isn't really intended to be used in the way he wants. Weddings are difficult enough to shoot without adding to the complexity. It is so easy to miss certain details that having a camera like a DSLR just enhances the possibility of missing even more. These are not controlled environments where you can tell people to wait. DSLR's can be amazing tools for weddings but you have to take in certain considerations to use them in those environments.
This is why I brought up getting a small low light sensitive video camera to use as a second camera. There are some amazing Panasonic video cameras for the price of the 14-140 zoom lens that spank that lens in low light shooting. They are have much better auto focus and power zoom. Just having a zoom lens doesn't always solve the situation. Manually zooming while shooting live can be a pain without a tripod to look decent. It can be done of course but it is much harder and takes more attention. Again a situation where you could potentially miss something. These small video cameras which are about the size of the 14-140 as well typically have a much broader zoom range as well which it virtually unheard of on a DSLR lens.
The fact is if you want a fast zoom you basically have two options each costing over $1,000.00. Even with those lenses you will have to swap lenses and can only zoom by twisting the zoom ring on the lens manually. Not exactly optimal for live shooting.
Can it be done? Of course but it takes a lot more effort with a lot more potential for error. This is where multiple cameras come in. A lot of amazing DSLR weddings are shot by more then one person with more then one camera. It tends to be the most and sometimes only practical way to get the job done. I'm sure there is somebody out there who does do it themselves with a single camera and that's great for them if they can handle the stress of doing it that way. In my experience a bride isn't going to give a darn about a bigger sensor if you miss the stuff important to her. It is the moments and guests important to her not depth of field and swapping lenses.
By adding a video camera you have a tool set with a wide range of practical uses. If you need to shoot a stage production you will be glad to have the power zoom with long reach. Need to shoot from the balcony at a church? The video camera will actually allow you to do that. No zoom lens is going to allow you to do this with stabilization, quick auto focus and power zooming. What you loose in depth of field control you make up for with sanity and happy brides.
Don't believe us talk to Jeff Harper at DVInfo. Long time GH1 and then GH2 user who shoots weddings. Finally bought a video camera to add to his five camera army of DSLR's he uses on every wedding by himself and he loves it. He bought a good 1/3" video camera which he says has been just as good in low light than all but his fastest primes. Jeff even considers f2.8 too dark for weddings so for him to be impressed with the low light on a video camera is saying something.
The Camcorder in question is the Canon XA10 virtualy the same as the G10 camcorder,no Panasonic camcorder has the low light abilities of these,apparently the new G25 has even better low light.