  Elementary particles are found in two different situations: (i) bound to
metastable states of matter, for which angular momentum is quantized, and (ii)
free, for which, due to their high energy-momentum and leaving aside inner a.m.
or spin, the $h$-quantization step is completely harmless.
  Perhaps Quantum Mechanics can be seen just as the simplest mathematical
formalism where angular momentum (the magnitude of each of its three orthogonal
projections) is by construction quantized: all possible values are taken from a
discrete set. Indeed:
  (i) This idea finds support in very reasonable, completely classical physical
arguments, if we place ourselves in the framework of Stochastic Electrodynamics
(SED): there, all sustained periodic movement of a charge must satisfy a power
balance that restricts the value of the average angular momentum, on each of
its projections.
  (ii) It gives a natural explanation of the concept of "photon", as a
constraint on the observable spectrum of energy-momentum exchanges between
metastable physical states, in particular also for its discreteness.
  QM would be, in this picture, a semi-static theory, transparent to all the
(micro)-dynamics taking place between apparently "discrete" events (transitions
in the state of the system). For instance, (the magnitude of the projections
of) quantum angular momentum would only reflect average values over a
(classical) cyclic trajectory, a fact that we regard as almost obvious given
the particularity of the corresponding addition rules in QM.
