I was a little surprised myself about continued use of AIFF. For better or worse, that industry adopted AIF years ago due to its usefulness with iTunes, ProTools, and tagging facility which WAV did not previously provide. Whole libraries are organized on that model so no amount of convincing can change what is established now.
This request for AIFF tagging is rather new and rare for us, so it is not a burning issue at present. But as music library delivery via CD declines, the need for files with embedded metadata will rise. Let’s see how things develop.