I think for pros who have much better control, what you see immediately (less than 1 video frame) post impact is more often an artifact of the type of shot desired than an intrinsic element of their swing. Just like shot pattern (draw/fade) most tour pros will have a 'natural' inclination but are still able to control trajectory as desired.
With IMA the trail wrist will necessarily straighten after impact (the next video frame). Scott says that it is possible to have a good (i.e. 'y') impact position with both wrists straight but this is a VERY short duration position and more likely to lead some to believe they're doing OK when they're not than to help IMHO. Scott does NOT say that both wrist need to be straight at impact (which is basically in the video frame containing impact).