And the fact that many REST applications depend on this faulty behaviour says more about those applications and their developers than it says about how things should be.
Perhaps ... But from a purely pragmatic point of view it would be a good thing to have :-), Personally, I wouldn't consider having an option "harmful" as long as it's off by default and documented, the problems from breaking standards usually arise from being undocumented and/or on by default ...
I'm not sure how much this "breaks" the standard though, HTTP is just one of the possible REST protocols ... Having REST requests outside of a HTTP context is not necessarily "wrong" or "not according to the standards" as far as I understand it ...