I think it would be nice to have deep sky objects integration in skyfield, like hipparcos database.
I have been maintaining OpenNGC database and it's python interface PyOngc for some time and I wonder if you're willing to consider a PR about using PyOngc as data provider for such objects. I think I can reuse most of the code of the Star class by moving it under a parent DistantObject class, then override specific code for Star and DeepSky.