I think there is a possibility in charging more for using the 5d but you have to provide something more to the client. An obvious extra service would be to use that big sexy sensor and take stills at the same time. Many clients would see stills as an extra that they would be willing to pay for.
As the division between still and motion shoots get more blurry it will be interesting to see how businesses adapt moving forward. Certainly the 5d will not be the last camera to offer quality video and stills in the same package.