> And, trivial to ignore or blindly carry it along if your software doesn’t specifically support it.
Which is about as good as not having metadata in the first place.
And since people rarely actually code to spec and it’s usual for wav files to not have metadata (and as demonstrated by GP common belief that WAV files can’t have metadata), pessimistically I would absolutely expect choking on wav metadata to be common.
There is no de facto supported standard because WAV files are de facto not used as anything but intermediate format these days. You could have fifty standards, that wouldn't change much.
WAV files can have any kind of compressed stream inside. A program that used some ancient API like WinMM ACM could theoretically play anything inside WAV as long as audio driver for that compressed format (now commonly called “codec”) was present. In addition, there are all kinds of standard metadata (like author and comment fields), and players in the '90s had no problem with displaying it in their interface if it was present. Old Windows Media Player had some of these status lines shown by default.
By the way, “driver” was an actual driver, with an .inf file, update of win.ini/system.ini or registry, and probably a reboot required to start using the decoder.
Old SDK tells us to look further into MMREG.H, so let's do just that.
It's interesting to look how all those early '90s ideas that Universal Tagged Formats would be used to hold anything and everything, and dragged-and-dropped into any and all application completely flopped. Mac had those, Windows had those, Amiga had those. You can say that MP4, an international standard, is actually MOV in disguise, but it doesn't support all those early crazy options that could turn the file into poor man's PowerPoint presentation, poor man's Hypercard, or poor man's FMV game. On the other hand, Windows Media Player did support ASF interactivity like “open the link in a browser at this timestamp”, “show user some text at that timestamp”, and the consequences were so bad that it all had to be killed in mid-00s.
There does seem to be at least some de facto standard, at least checking my collection for stuff I haven't converted to flac yet I found the Wingspan soundtrack in wav format with, according to kid3, an ID3v2.3.0 tag (including cover art) and RIFF info. It works with mpv and VLC, I didn't try anything else (well, I tried a couple of command line id3 utilities that didn't show the tags). I've seen tagged wav files a few other places as well so it doesn't seem super uncommon. However, checking quick it doesn't seem like flac notices the tags when converting.
It’s trivial to put a metadata chunk into that. And, trivial to ignore or blindly carry it along if your software doesn’t specifically support it.