I'm not sure if we should be going that far, but there may be cases where longitude and latitude are known with different degree of accuracy, so multiple precisions might be needed.
I think it's worth taking a look at what MaxSem has done with the GeoData extension, which is used for mobile apps, etc.:
GeoData uses globe, as that's consistent with how coordinate templates are done now on Wikipedia. I think starting simple and consistent with GeoData and the coordinate templates is good.
If no "globe" parameter is specified in the coordinate template, then Earth is assumed (and lat/long -- WGS84).
For the moon, selenographic coordinates are assumed and there are other reference "globes" for other planets and moons.
Perhaps things can get more complex later and having WGS84 coordinates wouldn't interfere with that.
Cheers,
Katie