In the case pywcsgrid2, ax[other_wcs] returns a new axes but with different transform. So, everything vector-based is supposed to work. Showing an image is quite different though.

pcolormesh, which is vector based, should work. But pcolormesh is quite slow unless you use agg backends.

Matplotlib now supports affine-transformed images (not for every backend but most of them), so we can support imshow by locally approximating the transform as an affine-transform. And my experience is that this is enough for most cases, but will not applicable for things like allsky plot, for example. Or we can regrid the image on the fly of course.