Due to my lack of time and to the fact that I am not sure whether this the right place to ask such a question I will post my question & my research efforts into parts, and continue expanding it depending on the kind of feedback I will get.
Part #1 (The basics)
I believe id3tags v2.4 is the most advanced standard for holding music metadata, with the downside that it can only be used on .mp3 (well, and some other) files, but not on lossless .flac files.
Question 1: Is anyone aware of a more advanced standard that id3tag 2.4. or something at least equally advanced that could also be used for lossless formats?
Question 2: Assuming .mp3 quality is enough and one doesn't care for lossless formats, is there some standard schema/way to add information in these id3 2.4 tags? I am not asking about filling in the basics, but about holding arrays of values and also using custom tags in a certain way that would facilitate the holding of as many information as possible. All this should be done in a way so that the metadata would be usable by at least some music players like musicbee, foobar2000 etc, cause obviously I am not planning to write a music application for now.
The above may not make total sense yet, but I 'll get into details and it will, assuming there are people interested to help create something concrete and also benefit from it themselves.
Part 1 Conclusion: id3tags 2.4 and .mp3 are for me the way to go on with this project. In any case, a big part of it is about semantics, rules and conventions, so for that part it shouldn't make a difference.
Part 2 (Filesystem VS Tag Metadata)
When it comes to computers every "local" music collection is actually a set of files, and files are organised in folders. Since file and folder names are usually not random, some of the information we want to pass on tags as metadata will also exist on our file and folder names. And to take this one step further, if file/folder names are correctly set in a specific way, they can also be used to auto generate the id3tag metadata in our music files, leaving only a subset of fields (the ones that contain the information that will only be on tags) to be completed manually later on.
Part 2 Conclusion: First thing to be done should be deciding which information we d like to keep, which will be kept on both filesystem and tags and which on tags-only, and set the proper naming conventions and constraints so that everything can scale without issues.
From this point on, as I am about to start getting into details, any feedback is really welcome..