Since electronic music exists that is under no obligation to reproduce or simulate instruments as if playing in a physical space, captured with 2 microphones, leading to inherent crosstalk etc. etc., there is always an expectation that arbitrary numbers of samples per track could be
100% L-R separated, and a good reproduction system should maintain that to the very limit of human capabilities to detect.
I could, just out of curiosity, but notice also the limits of what that experiment can prove, according to the author themselves:
No better than doing my own test with my own song, with a real-world (not synthetic) cable-change based alteration. And I detected differences that tell me -20 dB is far from sufficient, for me. But it's true that I only compared vs. -40 dB, since I only had the cables I had, and the difference I was hearing could have been realized anywhere in between. So it's not impossible that I have the same true threshold as the above author, that -30(?) dB happens to be enough for me as well, and that I was actually getting no extra benefit going from there to -40.
I imagine it would take a lot of work to set up a test to really clarify this - I would need to see what the frequency envelope of real-world crosstalk tends to be, if by any chance it isn't flat, then I'd have to set up some way to apply crosstalk
with that envelope to as many songs from my collection as I wanted, while also being able to tweak the amount of crosstalk from, say, -20 to -50 dB. And then listen and compare and listen and compare 'til I'm blue in the face.
Doesn't seem to be worth it, since all the gear I currently own is keeping me comfortably far away from -20 dB crosstalk, and if I ever think of getting any other ridiculously low-impedance headphones (or fall prey to the virus of IEMs) I will just take care to put them on a 4-wire SE cable at least (or better yet balanced), and that should have me covered. (Balanced is everywhere these days, so I don't expect a significant cost penalty for my insistence on having at most -40 dB crosstalk.)