One of the things third parties have to struggle with is that ballot access requirements are unevenly enforced - the deadlines, fees, signature requirements etc. are all draconianly enforced to the letter with minor parties, but the Republicans and Democrats are able to completely ignore them and the Secretary of State will put them on the ballot anyway. More than anything there should be a requirement that all parties must comply with the same ballot access rules.
But whatever would happen to states' rights?
I don't support federal legislation on ballot access obviously.