For example, in Michigan you have a lot of small businesses (even after 7 years of Granholm's purges). Many of them try to incorporate, but in all reality, they are really run as one man shows. That is, a corporation has to have a board of directors with real decision making power that meets regularly. Oftentimes, Joe Blow will incorporate a business and make his wife, kids, and the dog members of the board. So when the business defaults, and the creditors come calling, Joe can't absolve himself of personal liabilty if his business was not truly functioning like a corporation as opposed to a one man show.  

This "eligible" concept walks, talks, and quacks like a nomination. And depending on who has a beef with state party, yes I think they could sue and argue that the concept violates state law. If only one person per office is made "eligible" in May, they are for all intents and purposes being nominated in May as opposed to August.