I see a huge benefit for switching from opus to XHE-AAC for my audio books, where I have been, for the past 15ish years, targeting 18 kps lame mp3 vbr by using tricks of 7.8 khz low pass, 32 khz resample, mono, plus several other experimental switches that produced really listenable audio books that sounded better than most 24 or 28 kps mp3s. I might listen to 200 hours per month or more of audio books.
However, at the bare minimum I would need a really good Android XHE-AAC player with excellent navigation and memory of my place when my battery dies or any other playback interruption . Else, there is no point in the effort.
It took a while to find even one Android player that could remember my place (including vlc), much less play an audio book's tracks in the correct order (based on the correct file structure, audiobook/author/book/track number-title.ext), and have good navigation jump buttons.., Alex software Smart Audio book player, which does at least opus. But I doubt xHE-AAC, which is far superior for the desired bitrate for voice.
I have just started to use ffmpeg to record to opus. It seems superior to mp3, except for a hint of grain noise on the peak volume at <24, which I think might be annoying when listening in a car. I doubt I will be able hear it in a mono Bluetooth earbud in a normal environment, but I don't know yet.
I really would appreciate a good, functional xHE-AAC audio book player for Android.
I am assuming for now that there are none, and hoping someone will disabuse me of the assumption. I am coming up empty on Google.