So to answer the last part of my question I did a little experimentation myself. It seems if I copy just the block subfolder (including blocks/index) it still takes ages to start up, well at least an hour, I lost patience after that. But if I copy blocks/ and chainstate/ it starts up reasonably fast. Just a few minutes.

So I guess that's what I'd do if this ever comes up. No one can think of any problem with sharing the chainstate folder, right?