May I make a suggestion?
It was Abdus Salam who proposed that quarks and leptons should have a sub-quantum level structure, and that they are compound hardrock particles with a specific non-zero sized form.
Jean Paul Vigier postulated that quarks and leptons are "pushed around" by an energetic sea of vacuum particles.
David Bohm suggested in contrast with The "Copenhagen interpretation", that reality is not created by the eye of the human observer,
and second: elementary particles should be "guided by a pilot wave".
John Bell argued that the motion of mass related to the surrounding vacuum reference frame, should originate real
"Lorentz-transformations", and also real relativistic measurable contraction.
Richard Feynman postulated the idea of an all pervading energetic quantum vacuum.
He rejected it, because it should originate resistance for every mass in motion, relative to the reference frame of the quantum vacuum.
However, I postulate counter intuitive possibility, that this resistance for mass in motion, can be compensated,
if we combine the ideas of Vigier, Bell, Bohm and Salam, and a new dual universal Bohmian "pilot wave",
which is interpreted as the EPR correlation (or Big Bang entanglement) between individual elementary anti-mirror particles, living in dual universes.
So my prposal is based on a Rigid String Theory with real rigid strings able to mutate and merge by form based interlocking into leptons and quarks.
Photons and neutrinos are supposed to have a form shifting double life:
A: traveling with the local ( LASOF) speed of light as part of the oscillating Higgs field.
B: as real rigid string able to shift shape from Higgs into photon monopole or neutrino shape and interlock with (Lepto) Quarks