It is a lot of details to work out, which is why current AR headsets are still at the bridesmaid and not the bride phase.
VR headsets are workable, but somewhat expensive, and content is lacking.
AR headsets are very expensive, have poor image quality, and even less content. It seems every defense contractor and electronics conglomerate got patents for holographic waveguides in the 1990s when the F-35 was under development; that headset is not so bad but it costs $250,000 and the original version was heavy enough to break your neck when the election seat fires.
Apple may be working on an AR headset, it may be a big hit in the end, but I will believe in product-market fit when I see it.
I suspect they've tried to augment the device for AR already since many of the forward looking trends focus on AR.
If you are building an AR system there is always an awkward balance between "letting the environment shine through" and "having projected items be bright enough to be visible". If you put something black in front of the holograms at least now you have just one problem instead of two problems.