Apart from beauty, is there reason to believe the known forces to be parts of one "superforce?"
The response to a similar question seems incomplete in that it does not address unification; there is evidence to believe the forces all have the same strength at high energies, but to be the same force implies all matter is affected equally, which does not seem to be the case considering neutral particles are not affected by the electromagnetic force, and leptons are not affected by the strong force.
To imply that they are the same would there necessarily have to be some thought (or technologically-advanced) experiment in which forces can be "converted" into each other?
Take, for instance, the electromagnetic force. A charged particle stationary to an observer has only an electric field. If this particle is in motion relative to the observer the electric field is measured to be "converted" to a magnetic field, and charged particles experience a magnetic force if in motion relative to a magnetic field.
In other words, is it valid to say that analogously that if and only if there is some action(s)/frame(s) of reference that would make the other three forces measurable from some initial state in which there is only one then the four fundamental forces are part of a larger one?