I didn't use it, but it looks to me like one of the main draws of foobar2000 was library/metadata management. I've only ever used directories in the filesystem as a "library," and have used many players over the years (mainly moc, which I love, but which doesn't bring anything especially valuable to the table--I mainly just like the UI and out-of-box key commands).
Thus, to me, as an outsider, this whole conversation feels a bit like a cautionary tale about software/vendor lock-in.
Agreed, I've always made sure that any metadata or info I truly care about in my MP3s is embedded in them and independent of platform.
I like Foobar for some utility tasks, but I recently had to twist into a pretzel just to add a playback speed feature that at this point should be both standard and upfront in the UI, so I don't think Foobar is thaaat great.
I still use foobar2000. The library/metadata management it is quite proud of is entirely built on your existing folder structure (it does not mutate it; it auto-explores/watches it for changes) and your ID3 tags (which it only mutates on your explicit edits). That was a big deal at the time it launched, especially versus how Windows Media Player and iTunes both fought to control your folder structure, rearranged everything form time to time, and would update your ID3 tags at the whims of Microsoft's or Apple's "genius" tagging databases (which were often full of mistakes, especially for rare/weird files).
Foobar2000 was the breath of fresh air opposite of "software/vendor lock-in" and a model that software today still often fails to live up to.
Foobar had good options for using the filesystem as the library structure. Some of the options were user-made plugins rather than something available out of the box, but it all worked very well.
Thus, to me, as an outsider, this whole conversation feels a bit like a cautionary tale about software/vendor lock-in.