For having studied both classical and quantum optics, I regard Maxwell's equations as the grand "cheat sheet" from which (almost) all optical/photonic phenomena can be derived. Yet, I also know that wave-particle duality extends to all other fields and particles in the standard model. I'm therefore left with a nagging sense that Maxwell's equations should---up to differing units---be universal (cf. e.g., Gauss' law for gravitation).
I expect that some behaviors (say, the Aharonov-Bohm effect) won't be observable since some particles in the standard model are charged while others aren't, or that monopoles may exist while others don't, etc. That said, don't we have any evidence that the overall template of Maxwell's equations is universal?