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

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.