I would like the ability to setup a plot projection in MPL that can be defined by various parameters and does not need to be serialised as a string and registered with matplotlib.projections.register_projection. For example, an extension of /examples/api/custom_projection_example.py might be to add the ability to define the central meridian to an arbitrary value rather than the current value of 0 - in this case I would expect to define the projection by creating an object which can then be turned into a matplotlib axes:
hammer_proj = Hammer(central_meridian=45)
ax = plt.subplot(111, projection=hammer_proj)
I have made a change to matplotlib which would enable this capability, which can be found at https://github.com/PhilipElson/matplotlib/commit/9c7b1b27d0245a752d010bd03ae66dc6c000d8e499 . Any feedback and thoughts would be really appreciated with the ultimate goal of getting this functionality into MPL.