There has been a great deal of discussion of late about the impact of self-archiving on library journal subscriptions. Obviously, this is of great interest to journal publishers who do not want to wake up one morning, rub the sleep from their eyes, and find out over their first cup of coffee at work that libraries have en masse canceled subscriptions because a "tipping point" has been reached. Likewise, open access advocates do not want journal publishers to panic at the prospect of cancellations and try to turn back the clock on liberal self-archiving policies. So, this is not a scenario that any one wants, except those who would like to simply scrap the existing journal publishing system and start over with a digital tabula rosa.
So, deep breath: Is the end near?
This question hinges on another: Will libraries accept any substitute for a journal that does not provide access to the full, edited, and peer-reviewed contents of that journal?
If the answer is "yes," publishers better get out their survival kits and hunker down for the digital nuclear winter or else change business practices to embrace the new reality. Attempts to fight back by rolling back the clock may just make the situation worse: the genie is out of the bottle.
If the answer is "no," preprints pose no threat, but postprints may under some difficult to attain circumstances.
It is unlikely that a critical mass of author created postprints (i.e., author makes the preprint look like the postprint) will ever emerge. Authors would have to be extremely motivated to have this occur. If you don’t believe me, take a Word file that you submitted to a publisher and make it look exactly like the published article (don’t forget the pagination because that might be a sticking point for libraries). That leaves publisher postprints (generally PDF files).
For the worst to happen, every author of every paper published in a journal would have to self-archive the final publisher PDF file (or the publishers themselves would have to do it for the authors under mandates).
But would that be enough? Wouldn’t the permanence and stability of the digital repositories housing these postprints be of significant concern to libraries? If such repositories could not be trusted, then libraries would have to attempt to archive the postprints in question themselves; however, since postprints are not by default under copyright terms that would allow this to happen (e.g., they are not under Creative Commons Licenses), libraries may be barred from doing so. There are other issues as well: journal and issue browsing capabilities, the value-added services of indexing and abstracting services, and so on. For now, let’s wave our hands briskly and say that these are all tractable issues.
If the above problems were overcome, a significant one remains: publishers add value in many ways to scholarly articles. Would libraries let the existing system of journal publishing collapse because of self-archiving without a viable substitute for these value-added functions being in place?
There have been proposals for and experiments with overlay journals for some time, as well other ideas for new quality control strategies, but, to date, none have caught fire. Old-fashioned peer review, copy editing and fact checking, and publisher-based journal design and production still reign, even among the vast majority of e-journals that are not published by conventional publishers. In the Internet age, nothing technological stops tens of thousands of new e-journals using open source journal management software from blooming, but they haven’t so far, have they? Rather, if you use a liberal definition of open access, there are about 2,500 OA journals—a significant achievement; however, there are questions about the longevity of such journals if they are published by small non-conventional publishers such as groups of scholars (e.g., see "Free Electronic Refereed Journals: Getting Past the Arc of Enthusiasm"). Let’s face it—producing a journal is a lot of work, even a small journal that only publishes less than a hundred papers a year.
Bottom line: a perfect storm is not impossible, but it is unlikely.