I'm afraid that's probably never going to happen, at least not anytime soon.
The only way iTunes ever got created in the first place was because the Macs, unlike MS Windows, were so locked down and secured that Steve Jobs was able to convince the music publishers that it would be a safe and profitable platform with bare minimal risk of piracy. Something that was front and center back in the days of Napster and subsequent file sharing networks.
Once music publishers were convinced at how much money they could make, then having a less-than-100% locked down iTunes for Windows was still worth it for the much bigger market it represented while still making piracy a bit inconvenient (through he burning of music to CDs basically).
Any DRM copy protection that iTunes relies on, and the music licensors rely on, whom Apple relies on, would be broken in a hot minute by the Linux community.
Also, just about everything in Linux is GNU-licensed and open sourced. Apple couldn't have an iTunes product using any of the existing software tools, codecs, libraries, etc. without making the Linux for iTunes open source. Basically giving away the blueprints to the kingdom there. haha.
Someday hypothetically, if Apple Music subscriptions ever become the overwhelming norm could that change (making individual downloaded/DRM content sharing less of an issue) Maybe, but probably not anytime soon.
