I've recently heard of Wheeler's one-electron universe idea. Personally, I find it very beautiful and elegant, but I'm aware that there are any number of problems with it.
However, I'm curious why it's restricted to electrons. Surely, an antiproton looks the same as a time-reversed proton, and all protons look the same. Also, it would be a bit weird to have a universe with just one electron but plenty of protons. So, why not a one-proton universe?
Has this idea ever been seriously contemplated? If not, then what is fundamentally different about the two?
(If the key problem is that a proton consists of quarks, then how about a one-(top quark) universe or one-muon universe?)