There is if you don't want to lose advantages that following them bring. That said, I don't see how this would break any REST principles.

There's something wrong with breaking the semantics of GET; all the revision does is clarify that the syntax of HTTP is method-independent so that message bodies aren't syntax errors, but GET bodies still have no semantic meaning and ascribing one to them is likely to mean you server is doing things that clients, caches, etc., won't correctly handle.