The main place that needs the Euclidean position is the input to the `power_spectrum` and `nfw_halo` objects.  The functions `getShear` and `getMagnification` in both cases require a `PositionD` input, not a CelestialCoord.  So making this allow `world_pos` to be a `CelestialCoord` would mostly involve updating those classes.  It wouldn't be that difficult a change here in config.

The other possible application of `world_pos` being a `CelestialCoord` is if people want to place galaxies on the image according to their RA and Dec.  I suppose if that use case is desired before anybody wants to update the lensing classes to allow for celestial coordinates, we could delay this projection until the calls to `getShear` or `getMagnification`.

I think in both cases, I'd rather wait until a use case develops before trying to implement either one.  Maybe when I update the Config wiki page with all this new functionality, I'll put a little note in about `world_pos` that if you would like to have RA, Dec coordinates for `world_pos`, please open an issue about your use case, and we can make it happen.