i dont think the hatch is too much worse than the coupe. i think with a cage and some decent bracing between rear strut towers it should be good to go.

if u look at the differences, the coupe has the rear deck and slope where the back portion of the rear seat meets that metal and it has more of a trunk, less side window and less rear window. but the hatch is i guess floating (since it opens it doesnt solve flex between the two hatch "rails" (rails = where the hatch sits on the body) so maybe welding that shut or bracing it near the inner part of the taillights would help but that would go along with a complex cage.

also the coupes are lighter to begin with, so if someone was to try and make a hatch more rigid, they would remembe that:

weight of coupe with cages, etc < weight of hatch with same