Words are just labels we attach to concepts that we find ourselves wanting to refer to. My claim is that there is no concept in allopatry that's worth naming.
Have a look at Hey's underappreciated book (he's the first author cited in the article you linked).
It is an embarrassment: because there's a simple answer (the one I just gave), and because the confusion over "species concepts" has persisted for decades and confused generations of biologists, and hundreds, if not thousands of flawed papers have been published claiming "sufficient divergence" of allopatric populations.