I think I'm with @leejjoon on this one, but even further ;)  `astropy.wcs.WCS` is one implementation (`wcslib`) of one representation (`FITS WCS`) of WCS.  In fact, once we can make such a change, I'd almost want to rename it to `fits_wcs` to help distinguish it from the more general WCS that are sure to come...  I think I'd prefer they were independent models.  I can envision this plotting work being extended in the future to have different transformation backends, the first being `astropy.wcs`, but many to come in the future.