I think you are saying to create an MLT file with only the video and replaced audio joined by an audio mix transition. Then, open that MLT file as a clip in Shotcut? That might be a clever way to do it. But I think some people might have multiple video angles as well that they would want to synchronize.
I think it would be good to have a way to set one track as the “reference” audio track and then align all video clips on other tracks according to the reference. As long as you edit with “ripple” enabled, the clips will say synchronized as you edit.