From Richard Winger at Ballot Access News:
Earlier this year South Dakota changed the petition deadline for a newly-qualifying party to submit a petition of 2.5% of the last gubernatorial vote for party status. The old deadline was March 29. The new deadline is March 1. On June 15, the Libertarian Party and the Constitution Party filed a lawsuit against that deadline, Libertarian Party of South Dakota v Krebs, 4:15-cv-4111.
South Dakota is in the Eighth Circuit. In 1977 the Eighth Circuit said in MacBride v Exon, 558 F 2d 443, “It is completely unreasonable and unrealistic for a state to provide by statute that a person cannot get his name on the state’s presidential ballot as a third party candidate unless that party has qualified as a party in advance of primary elections.” Currently, South Dakota is the only state in which it is impossible for a new party to appear on the November ballot with a presidential candidate and the party label, unless that party participates in a primary. The South Dakota primary is in early June. MacBride v Exon was a Nebraska case, and the Nebraska primary was (and still is) in May.
UPDATE: here is a news story about the lawsuit.