FWIW cartopy has implemented this kind of functionality, without the need to wrap all Axes methods, by using the ```transform=``` keyword. So:

```
import cartopy.crs as ccrs
ax = plt.axes(projection=ccrs.Mollweide(central_longitude=180))
plt.contourf(data, lons, lats, transform=ccrs.PlateCarree())
ax.coastlines()
plt.show()
```

This has the added benefit that the standard pyplot interface can still be used.