If that were wood, scraping sanding and glassing inside might be a lot more awkward. One also has to consider hatches. And cockpit coamings. I know many folk here like to get all that work done before mating the halves.

If you do the scraping and sanding while it's on the forms, then seems like it'd definitely be harder to do that with the female forms. I don't see it as a problem for the "half-shell" approach over regular forms, though. If anything I think access would be improved.

Hatches and cockpit coaming, though - that could be an issue. Also, installing bulkheads might be significantly more difficult.

I suppose this could be resolved by slicing horizontally rather than vertically - that is, establishing a flat rubstrake line that becomes the attachment point. I believe I saw Nick doing something like this anyway (on a regular form of course) - rather than splitting at the sheerline he included the upper hull as part of the "deck" assembly because he was dealing with a tumblehome hull shape. So there doesn't seem to be anything magic about the sheerline as the separator.