Figuring out what limits light to 186,000 MPS would go a long way to faster-than-light stuff.......
AFAIK, SOL is determined by the relative permeability of empty space to the electric field and the magnetic field.
Maxwell type stuff.
It’s predictable from numbers we can measure, but we can’t measure those numbers to any greater/less accuracy than we can measure the SOL.
Sort of like people ask if we live in curved space or flat space.
There is really no difference because straight lines in curved space are the same thing as curved lines in flat space.