Coming Now to a University Near You
This is actually a pretty common practice and has been for some time. If you've been on the job market for two or three years without a book published or at least contracted, you're usually considered stale goods.
This predictably results in a mad dash for adjunct or visiting professorship positions, where you publish like mad before your 1 or 2 year appointment is up. Those who succeed may
get a TT job. Those who don't...well, you don't see anything from them anymore. Some people manage to get a TT job after hopping from one temporary position to another. Getting a job after being out of academia for a few years, though? Pretty slim chances.
I'm not sure this should caution students against going to graduate school at all, even in the humanities. Rather, I think it simply serves to emphasize the importance of (1) going to the best possible program you can and (2) having a fallback plan in case you don't get a job in academia. Success rates in academia, especially in the humanities, really aren't very evenly distributed; some programs do far better than others. For example, you may have places like Yale and Chicago placing 100% of their graduates in medieval English in TT positions, USC and UGA placing 40%, and Western Rural Regional State U only 10% (to make up random numbers).