Of the two, there's a lot clearer line to Apple open sourcing some of its core desktop apps, given market share (~16%?) and lack of internal resource prioritization (iOSiOSiOS).
The best time to do so would have been ~2010, after iTunes revenue provided a clear monetizable carve-out.
The second best time would be today.
The number of people saying 'I love the hardware you sell me, but am switching platforms because your software is trash' should be a flare that even Tim Cook can notice.
And anything that moves MacOS closer to OSS should be welcomed by Apple -- it's their easiest (and most affordable) path to competing with Microsoft (Azure) on desktop.
Or if they would just embrace Asahi! Have a team work full-time on parity, have asahi-linux feature complete on Mac launch day; mainlined soon thereafter.
We can dream.
I mean, there's more of a rationale there. If they cede complete control of the OS, then that starts to eat into their services business.
And it's hard to pick a middle ground once they open up the OS.
At least with apps, there's a clear dividing line between this app and that app.