This is an interesting idea possibly for executive search maybe? I don't see it making much sense for contingency though for several reasons, the key one being time. When you have a hot search, time is of the essence and you need to get your best candidate over to your client ASAP, and if you have a really tight and trusted relationship you get interview slots so you skip the step of having to send anything to the client for their initial review, they trust you to do that screening, knowing the people are more than just a piece of paper....or a video.
For the time factor, I also don't see the clients wanting to take the time to review all this material before an initial interview is scheduled, this is what they are paying us to do. Also, this is time consuming on behalf of the candidate, and frankly, the best candidates won't want or need to be bothered to do this.
We always want to get the candidate in front of the client for a face-to-face as soon as possible. Using this video will slow down the process and more than likely will screen more candidates out than in, as the majority of people are not truly comfortable in front of the camera, so a mock interview like this won't give the client a true feel for who they are.
Just my take on it. It may be an effective tool for some scenarios.