May 19 2019
May 16 2019
May 12 2019
May 4 2019
Well all the edge cases you listed need to be correctly handled and tested, and that is a significant effort.
You sure forgot some of them:
Apr 25 2019
It seems to me that the list of edge cases out-weights the potential usefulness of such a feature, so I would consider that very low-priority at the moment.
Note that you can just group both clips together to make them move in a coordinated way. Note that for now there are no group effects, so effects would still need to be applied to both halves of the clip.