Michigan independent gubernatorial candidate Todd Schleiger is already campaigning, even though the election is not until November 2018. See this story.
Michigan has never had an independent candidate for Governor on a government-printed ballot. The only other states for which that statement is also true are Delaware, Hawaii, Indiana, Montana, New Mexico, and North Carolina. Schleiger will need 30,000 signatures, and he can only collect them in a six-month window of his choice.
One reason Michigan has never had a independent candidate for Governor on the ballot is that the state had no statutory procedures for independent candidates until 1988. Another reason is that the petition is as difficult as it is.
If Schleiger gets on the ballot, his campaign will be helped if the straight-ticket device is gone by 2018. The legislature repealed it in late 2015 but a court restored it on the 2016 ballot because the judge believed the straight-ticket device repeal injures black voters. The case is still pending in U.S. District Court, and the state recently filed its answer.