It was confusing to me at first, yet after a while I believe I started grasping what the translation is about. My current thinking is that it is mostly about making sure that the most important parts of artistic intent get through even the most inaccurate varieties of audio delivery chains.
It is not so much about trying to tune a record to this generalized end user system and also to that generalized end user system, but rather about making the composition outright simpler and cleaner, so that it has a good immunity against severe distortions.
Examples: Frequency range is cut. Dynamic range is reduced. Subtle echoes are removed. Emotions-conveying voice overtones are kept in check. Vibrato, chirps, and other effects based on frequency modulation are avoided. Genuine transients are replaced with noise bursts.
Well, there are different approaches. Used for many decades. So as examples I'll use some pioneering ancient compositions, expressing the approaches in very pure forms.
Some of the songs are just made super-simple. Like "Fly, Robin, Fly" by Silver Convention:
Those translate to everywhere, and that's the single high fidelity version. A lot of pop music and EDM is done that way to this day.
A more subtle approach is to make a composition simple and clean enough to translate well, yet still keep some of the subtleties in a softer form, to be safely sacrificed while delivering through less resolving chains, yet still available from the same record to more discerning listeners.
One of my favorite examples of the subtler approach is Popcorn by Gershon Kingsley (apologies, you'll have to go straight to Youtube to see it):
Composer's own rendition illustrates the artistic intent even better:
Apple ear buds, when new and connected to an iPhone, are much more consistent than the 6x9s, made by many manufacturers, driven by various head units, in vastly different car acoustic environments. I understand why sound engineers prefer mastering for the ear buds rather than for car stereos.
I think this is a great idea, and may fully flesh out one day. Hybrid SACD releases, and multiple Blue-ray audio options on a disk are approximations of that.