I would think this would be handy but only for a handful of people, of the say 1 million FCP users I would think less then 1 percent would like this feature so it might be a hard sell. Log and capture/transfer pretty much does nothing to the footage right now, except for maybe changing the codec so I would not hold out much hope for this.
Like you said most systems now have a prism to fit this in the field.
I think want might be easier for a programmer would be to write some kind of Flip that can batch process the clips after capture and that way it would still have the TC and you have to render the clips in FCP.