Hi vacuodynamic,
A quote from the book, Gravitation by Misner, Thorne and Wheeler (page 1215) relates to your post, "What else can a (subatomic) particle be but a fossil from the most violent event of all, gravitational collapse?".
If a proton particle is in fact, formed by gravitational collapse, then we would expect that it is gravitationally confined just as the electron appears to be. The proton is a more complex particle than the electron, so it may some significant time before relationships (equations) can be developed that could give substance to the concept, that the proton is black hole related.
We may be quite close however to defining the relationships to show that the muon is black hole related.