The idea of “hadronic supersymmetry” originated in the mid-1960s and derives from the observation that baryons and mesons have similar Regge slopes, as if antiquarks and diquarks are superpartners. This is most efficiently explained by supposing a QCD string model of baryons in which a diquark substitutes for an antiquark at one end of the string, but there are superstring models in which the baryon-meson relationship is a genuine supersymmetry.
In 2005, Alejandro Rivero proposed that mesons are to leptons as diquarks are to quarks. If the top quark is excluded from consideration, as too heavy to hadronize, then one has enough quark-antiquark pairings to match the electromagnetic charges of all the leptons, with a few leftover u,c pairings with charge ±4/3.
The construction is a little complicated, but the possibility that supersymmetry is already right in front of us is so amazing that it just cries out to be investigated. I have an ongoing discussion with Rivero, about whether his correspondence might be realized in a preon model, or a "partially composite" model, or a sophisticated string-theory construction.
Meanwhile, I'd like to know, is there some reason why this can't be realized? The closest thing to such a reason that I've seen is found in comment #11 in that thread: "For a SUSY theory, not just the spectrum must be supersymmetric, but also the interactions between the particles." So far, all Rivero has is the observation that some quantum numbers of diquarks/mesons can be correlated with some quantum numbers of fundamental quarks/leptons, just as if they were elements of a single superfield. I suspect (but I'm such a susy newbie that I can't even confirm this) that you could realize the correspondence in a QCD-like supersymmetric theory, if it was first expressed in terms of meson and diquark variables, and then supersymmetry was completely broken (see comments #40 through #44), but that this would somehow be trivial.
Nonetheless, I think the possibility that supersymmetry is already right in front of us would be important enough, that someone should investigate even such a "trivial" realization of Rivero's correspondence, with a view to understanding (i) whether such a "hard" form of susy breaking might realistically occur (ii) how it would affect the various roles and problems associated with supersymmetry in contemporary physical thought (protect the Higgs mass, supply dark matter candidates; technical model-building issues like "the supersymmetric flavor problem, the gaugino mass problem, the supersymmetric CP problem, and the mu-problem"...).