For one thing, an expected field of candidates that could be both broad and deep has led some to predict that the DFL convention will deadlock on endorsement, as it has in three of the last five election cycles, including the one in which Rybak triumphed as an unknown.
For another, the city's switch to ranked-choice voting throws a wild card into the process because there's no primary to winnow candidates, and the second and third choices of voters could determine the winner in a large field.
And if the turnout approaches the highly competitive 1993 election, there will be twice as many votes to count -- possibly by hand -- as in the 2009 debut of ranking city candidates. With a hand count, the new mayor's identity might not be known for several weeks.
Already declaring candidacies Thursday were Council Member Betsy Hodges and former Council President Jackie Cherryhomes, out of office since 2001 but still a City Hall player as a lobbyist.
Hodges created a campaign committee on speculation that Rybak might not run; Cherryhomes said she'll do so once she returns from vacation.
Council Member Gary Schiff, who was considering taking on Rybak, said he expects to decide on a run in the first half of January. School board member Hussein Samatar said he'll decide in the next two weeks whether to run. Park Board Commissioner Bob Fine said he's considering a bid.
City Council President Barb Johnson said she isn't running, saying she considers herself more effective in her present role.
"I don't think we've seen the full roster of candidates yet," said Tony Hill, a University of Minnesota Duluth political scientist and a student of Minneapolis politics. Some expect a dozen or more candidates, and with ranked-choice the second preferences of those polling poorly next November could determine who gets elected.
Some already compare the upcoming election to 1993, the last election when a politically popular incumbent, Don Fraser, retired and prompted a scramble for his seat.
That year's field included two council members, a county commissioner, a legislator, a mayoral aide and a businessman. There was no endorsement by the DFL, and Sharon Sayles Belton emerged as the city's first female and first black mayor.
Rybak himself could be a key factor. "I expect to play a large role in this election, but I don't expect to endorse for a while," he said Thursday.
He's probably politically closest to Hodges, who shares the vote-rich southwest corner of the city with him, but also appointed Samatar to the Library Board.
Schiff could be expected to draw support from the progressive wing of the party as an ardent opponent of Rybak's stadium proposal.
Hill suggested that Rybak's political career isn't necessarily over. He was the runner-up in the party's 2010 gubernatorial endorsement contest, and current incumbent Mark Dayton didn't run for a second term as either state auditor or U.S. senator.
"[Rybak's] kind of leaving with trumpets blowing, and he didn't get ensnared in any major scandal," Hill said. "I think Rybak is in good shape for the future if he wants to run for governor in 2013."
Steve Brandt • 612-673-4438