I agree with keeping maintenance down, but that’s the thing: there isn’t really 1 standard. There are loads of files out there with base 5, 10, 100, 255, … If you just let the user set the scale max that’s used for the normalization to base 10 during sync instead of guess-mapping it, no one will have to come for support as any 0-linear convention would be supported without error. I think your base 10 in the db is an excellent choice for a scale (database or otherwise) and I’d even like to adopt it, but as you just said, heuristics actually breaks all scales up to including 10 instead of helping with them.
Is your position that you want to push base 100 as the golden standard to be used? Is it really that common already across all kinds of platforms and tagging apps? I’m fine with adopting that convention but I’d like to be sure it’s really a dominant standard and not just another vendor flavor before I do, and I don’t use any clouds or such for my music so I honestly have no view on it.
Either way, it would be great if symfonium’s requirement on the user to use base 100 ratings was clearly indicated in the gui and docs, along with which tag key names are supported for it (rating, popm, popularimeter, …) and other display properties. Foobar for example lets you customize the name mapping, which of course I’m not asking for symfonium to do, but knowing which names are read for what attribute is pretty important. Disc and disk, tracknumber and track number, …
My suggestion for the raw value was to serve 2 secondary purposes really: on the one hand show that a file’s flavor of tag naming works and the value is read, and on the other to support filtering regardless of scale (by normalizing the search value by the same logic, since I now know about the normalization before saving to db). This isn’t important if the ratings just work instead.