Illinois Representative Mike Fortner (R-West Chicago) has introduced HB 5913, which would establish a top-two primary in Illinois. The bill, as introduced, seems to include the presidential primary. If it does, then in November 2008, the only two presidential candidates who would have been on the ballot would have been Barack Obama and Hillary Clinton. Illinois already has an open primary, and any voter was free to choose either the Democratic, Republican, or Green primary ballot in Illinois in 2008. Obama received 1,318,234 votes; Clinton received 667,930; John McCain placed third with 426,777 votes.
Illinois has the earliest primary (for congress and state office) of any state except Texas. Candidates in Illinois primaries for 2014 were required to have filed on December 2, 2013. If Illinois had a top-two system, all routes to the November 2014 ballot would be closed off in early December 2013 (except primary write-in candidates could file a declaration of write-in candidacy in January 2014). Under current law, independent candidates and the nominees of unqualified parties can petition onto the November 2014 ballot by June 23, 2014, but that route would be blocked off if HB 5913 passed.
HB 5913 appears to prohibit counting write-in votes in November. It says no candidate can be certified for the November election except the two who came in first and second in the March primary. So even though the bill does not delete write-in space from the November ballot, it appears to block anyone from filing as a declared write-in for November.