Anthony Towns wrote about user configuration (i.e. ~/.foo) and the XDG spec/proposal versus his own (and according to him) simpler version. The main goal of all this is to get rid of all the ~/.foo directories and files in a users home directory. Apart from technically minor differences, I don’t see why AJs proposal would be simpler than the XDG approach. All it does is hardcoding the values which are adjustable in XDG via XDG_*_DIRS.
There is one notable difference though: AJ proposes fallback values which are compatible with existing application paths (i.e. HOME_ETC/XDG_CONFIG_HOME should default to ~/ – resulting in ~/.foo files/dirs). This is a good proposal in a way: If you patch an existing application to strictly follow the proposal made by AJ, it still finds its old configuration (and other files) if the new environment variables are not set. No need to move anything around. However, I think the XDG approach is better since it makes sure that compliant applications don’t clutter ~/ anymore. They do need some mechanism to move existing configurations and data around though if the XDG-compliant stuff isn’t already there, but an old style config exists.
All in all, I think it is worth following the XDG spec, even if it is slightly more complex than AJs proposal. For one, it already exists for a while and I think that some applications already started following that spec. It also makes slightly more sense to me to have the system fully configurable as to where the apps store data as opposed to the hardcoded fallback/default values AJ proposes (even if we would change AJs proposal to use “$HOME-cleaning” default values).