I notice the $XDG_DATA_HOME environment variable isn't set in my Intrepid install. Maybe its set in later Ubuntu version.
But the value not being set for me means implies to me that it not being set is pretty common. Thus it seems like supporting this standard is going to involve supporting a fall-back of whatever you would do otherwise.
So I don't see "easy" at all but rather extra BS. Sorry.
From the spec: If $XDG_DATA_HOME is either not set or empty, a default equal to $HOME/.local/share should be used. Similarly there's a default (.config/) defined for XDG_CONFIG_HOME. So the fallback is well-defined rather than "whatever you would do otherwise".
Also, for my 2c, you should consider updating your Intrepid install if you at all can. It hasn't been supported for over two years, so it hasn't seen any security updates in that time. The Ubuntu do-release-upgrade system is pretty easy and reliable.
But the value not being set for me means implies to me that it not being set is pretty common. Thus it seems like supporting this standard is going to involve supporting a fall-back of whatever you would do otherwise.
So I don't see "easy" at all but rather extra BS. Sorry.