Just to be clear, I don’t really mind which direction this goes, I just think one is more intuitive and potentially more useful than the other. I even went through a short period of removing Soundtrack types from Single release groups myself:
Three years ago, when reading the guidelines, I inferred (largely from the Work style page and a forum post by Reosarevok) that Singles weren’t generally to be considered soundtracks. Thinking this could be made more explicit, so editors don’t have to go to the trouble of cross-referencing various pages and coming to their own conclusions in the future, I thought I’d try and improve the documentation with this wiki edit to the ReleaseGroup/Type page. It was eventually reverted by Reosarevok in this edit, with the following explanation:
“The conversation mentioned for this change is about works. For RGs this is not really the case – I’d expect a single clearly marked to be from a movie soundtrack to be listed as such.”
So that’s how I’ve been doing it since.