> journals should not be the arbiters of quality

It is the editorial board, i.e. academic peers, not the publisher, that are (?were) the arbiters. As far as I can see, the primary non-degenerate function of journals is to provide a quality control mechanism that is not provided by "publishing" on your own webpage or arxiv.org. If journals really are going to abandon this quality control role (personally I doubt it) then I fail to see their relevance to science and academic discourse at large.