I vaguely remember the 24bit thing as well, though it wasn’t important for me. But does ALAC do 5.1 now? I have a few music BD rips that are 5.1 in FLAC and when I converted them back then they were randomly either silent or completely scrambled, idk what was up with that, but it appears it wasn’t supported at all.
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Apple Lossless supports up to 8 channels of audio at 16, 20, 24 and 32 bit depth with a maximum sample rate of 384kHz. – Wikipedia
I can see how, as a business trying to operate on a budget and meet deadlines, adding support to iTunes for an obscure audio format that serves the same role as ALAC and can be easily played by other software is going to be low on the list of priorities.
I imagine since FLAC support has been creeping its way into other Apple software, iTunes support may be somewhere in the pipeline. I wouldn’t hold my breath, but I don’t think it’s entirely out of the question for it to eventually be a thing.