Barring that these outperform any and all existing Apple headphones by a significant margin, the main point is that these are probably so good that even Apple reaching parity with them in sound quality, noise cancellation and build quality would be a significant step up for them. At the high end - where Apple hasn't been before - the bar is already so high that any gains are baby steps.
The WH-1000XM3 is pretty neat but I don't see how they can be seen as a paragon of sound quality, particularly with their quite exaggerated bass response.
They're not high-end by any stretch of the imagination. They're good BT headphones, certainly a lot better than most, but I don't see why any BT headphones right now would qualify as "high-end" and there are others which are at least just as good in technical terms as far as SQ is concerned (there are plenty of measurements around the web to demonstrate that). I don't see any challenge here for Apple to match any ANC BT headphones on the market right now as far as technical capabilities are concerned, particularly given their track record with the APP or the Homepod. The big question is how they'll tune it. So far the APP or HomePod suggest that Apple won't go for extreme biases as far as FR goes but the end result may still not be to everyone's liking (personally I don't
love either one of them but I don't actively dislike them which is a progress vs. most other BT headphones or entry-level wireless speakers).
Their ANC works well but is limited in frequency, where they truly shine is in combining it with excellent
passive ANC. There is some evidence that the APP's ANC system is already working harder than the WH-1000XM3 at higher frequencies in a tiny package (and it has to given the APP's much worse passive isolation). I think the end result will depend a lot on what Apple wants to do in regards to passive isolation / vents design and allocation of computing resources / power.
Also, in general Apple doesn't really seem to care about sound quality. They still offer no lossless tier for Apple Music, and their phones don't even support a high quality lossless transmission codec. Apple is more concerned about convenience and ease of use.
The Who's Who's Next version on Apple Music begs to differ. I'd rather listen to this master than other commercially available ones in lossless audio. Heck, even Uptown Funk's master on Apple Music is a lot better than on other commercially available platforms.
AAC can be a good enough BT codec for A/B comparisons... provided it's designed and used well (which it rather is in Apple products but not elsewhere - implementation quality varies widely unlike other codecs and goes from total crap to CD SNR). Given the current state of BT headphones you'd probably be at a loss to A/B blind Apple's AAC implementation with APTX-HD or others. AAC is very different computationally wise anyway than most other BT codecs.
It would be nice if Apple provided a lossless option on Apple Music but let's face it... these days lossless files are listened to on systems that are nowhere near precise enough to begin with (I've yet to see a pair of headphones that can reach a FR target within 1-2db across the whole range in narrow bands).
There's plenty of evidence that Apple does care a tremendous lot about sound quality in general, as their laptops easily demonstrate for example (this is something that's never really going to embellish a spec sheet and yet they spend resources on that without flinching).
But it's quite likely that in specific terms, in some areas, they're ready to make compromises to the advantage of other variables. I'm pretty certain, for example, that comfort, size and weight were given priory n°1 for the AirPods Pro and that the SQ team had to work around these constraints (and IMO they did a pretty decent job at it).
Personally I'd have a much more nuanced opinion on Apple's dedication to SQ. It's just that they're, mostly, a general consumers company and will allocate resources holistically to make an overall attractive product instead of putting it all into SQ alone. With exceptions they don't do niche products, such as $15000 speakers or $3000 headphones. But if they did I see no reason whatsoever why they wouldn't be able to provide competitive products.