Stereo sound was designed for speakers at a certain distance/angle to the listener. It is now uncommon for people to have such setup, as many people listen either with headphones, or casually (mono speakers, or randomly arranged stereo speakers). While it is possible, it is very rare for people to have a stereo-to-binaural setup (see a related question).
So, should audio tracks be designed for headphones (binaural)?
Is it perhaps already commonplace?
Are there standards on how to add information to audio tracks so a conversion can be attempted (or not) on the fly?
Given the difficulty of mastering and distributing music in both formats, what are the pros and cons of the two options from practical and sound fidelity point of views?