Non-exclusivity is an inevitable pre-requisite of a multiple-media publishing environment, an opportunity that most academic authors are experiencing for the first time. Publishers might not offer it, but authors can demand it. Publishers can still be assigned rights, but not necessarily exclusive rights or 'all rights'. This does not preclude e.g. exclusive print rights. But beware, a bigger hurdle to publication in a prestigious journal is where the author has to vouch that an article has not been published elsewhere. 

Non-exclusivity requires some control of versioning to prevent undesired proliferation of different copies of a work, but this is not strictly a new problem and academic culture will adapt to instil good practice.