My use case involves doing revision comparisons between two tags (each representing a successful build) for projects based on GH.

Via command-line, the way I could get the right behavior was (where test-1.0.1 and test-1.0.0 are tags created by a separate process unrelated to my particular jenkins job)

$git whatchanged --no-abbrev -M test-1.0.1 ^test-1.0.0

Using the plugin with the remote branch required only allows something like:

$ git whatchanged --no-abbrev -M test-1.0.1 ^origin/test-1.0.0
fatal: bad revision '^origin/test-1.0.0'

Perhaps there is some other trick that would allow me to gain the same effect, but I don't see the downside of this improvement in any event.

Note that the current documentation for the behavior is:

Using this behaviour will preclude the faster git ls-remote polling mechanism, forcing polling to require a workspace thus sometimes triggering unwanted builds, as if you had selected the Force polling using workspace extension as well.

 
So, since the plugin already requires a workspace and cannot compute the changesets solely on the remote side, I see no advantage of requiring a remote name.