The point of regressplans.sh is to see if anything goes seriously wrong when forcing non-default plan choices --- seriously wrong being defined as crashes or semantically wrong answers. It's not expected that the regression tests will automatically pass when you do that, because of their dependencies on output row ordering, not to mention all the EXPLAINs. I'm not for removing it --- the fact that its results require manual evaluation doesn't make it useless.
It might be worth post-processing results files to ignore row ordering in some cases to allow for easier comparison. Has this been proposed in the past?