The Standard Model encapsulates all we know so far of the material world: that there are 12 matter particles (the electron being the most familiar) and 12 kinds of particles that transmit the forces between these matter particles (the photon being the most familiar). To these, we must add the most recent particle celebrity, the Higgs boson, found in 2012, and the hypothetical graviton, the particle that supposedly transmits the gravitational force. ...SUSY would more than double the number of particles.
Lykken and Spiropulu give an excellent illustration of the struggle, quoting noted physicist , from the Institute for Advanced Study:
"What if supersymmetry is not found at the LHC?" he asked, before answering his own question. "Then we will make new supersymmetric models that put superpartners just beyond the reach of the experiments. But wouldn't that mean that we would be changing our story? That's OK; theorists don't need to be consistent; only their theories do."
The question, though, is how long can you keep on changing your story before you realize the story is just wrong? This is the hardship (and the excitement) of research; we don't have a path ahead, we need to forge one. And we are not sure of which direction to take, having only inklings that it could go this or that way.
I think the Standard Model count is already high. There are 3 families of fermion particles, but maybe they are just different states of 1 family. Maybe the electron is just a charged neutrino. Maybe the up and down quarks just differ by charge. They have different masses, but that might be attributable to charge.
There are 8 strong bosons, but there is an SU3 symmetry that relates them all. And a SU2 symmetry relating the 3 weak bosons.
So maybe there are only 6 elementary particles: the down quark, neutrino, photon, strong boson, weak boson, and Higgs boson. There are also anti-particles.