nathanimal

1. Only high end headphones, with a high-end amps connected to high-end DACs (we're talking about systems in excess of $2G's) in a critical listening environment, can begin to resolve the differences between lossless encoded 96kHz/24-bit audio and music that is properly encoded for 256kbps HE-AAC using Apple's Mastered for iTunes guidelines. Even then, only highly trained listeners can hear what very minuscule differences there are.

2. The iPhone is a PORTABLE listening device, that many people use in sub-optimal listening environments. (Noise cancellation circuitry carries a slight fidelity penalty in order work its "magic".) Also consider that the headphones which are most capable of resolving high resolution audio are almost always open-backed (which lowers cavity resonances and improves fidelity), and have no noise isolation whatsoever. Almost all iPhone headphones are closed-back. The listening environment factor alone negates any possible advantage that high resolution audio can offer. 

3. No sub-$300 headphones (the most money most people are willing to spend on a set of cans) will be able to resolve high resolution audio in an audible way, even with higher-end DACs built into the headphones and amps power from the iPhone. And as it turns out, bluetooth headphones already have these electronics in them, albeit for 44.1k/16-bit audio in most cases. In fact, many of the customers who buy higher-end headphones usually opt for bluetooth, preferring a cordless experience.

4. The data overhead of lossless 96/24 audio is often 10 times (or more) what 256 kbps AAC is. Distributing that to millions of listeners requires pretty significant infrastructure. Which may or may not already be in place as far as Apple in concerned. Again, all this would be for a very negligible increase in fidelity that only a very small percentage of customers can actually take advantage of.

In much more brief terms, encoding algorithms and data rates are far from being the weakest link in the audio delivery chain - past a certain point (which is, surprise-surprise, 256 kbps AAC). Most important is the listening environment; followed by the transducers (headphones), amp and DAC; followed by PROPER encoding (no re-encoding 128 kbps AAC, which is still an issue for a significant amount of iTunes Store/Apple Music content); and then, going up to 96/24 helps that last 0.00001% of fidelity. 

In other words, Apple will almost certainly not change their current trajectory when it comes to audio delivery. 

But if they do, they'll do it because it will be a selling point to differentiate themselves, which is fine. They have billions in the bank to do it. Pretty much NOBODY will hear the difference, but they will THINK they hear a difference, which is all that matters in marketing. :-)

Sorry if anybody is rubbed the wrong way by my not citing any references... I'm lazy, I'll admit it. So you'll just have to take my word for it that I know this field and market very, very well.