This AP story on Montgomery County's last-ditch effort to keep the Barnes from moving to Philadelphia includes the following from Harvard lawprof Bruce Mann:
"The commissioners don't have standing to sue, and too much time has elapsed, he said. 'There's no part of the judicial system that permits do-overs years after an issue has been adjudicated just because someone steps up and says, "Hey, I have an idea,"' said Mann, who has followed the Barnes case. 'The fact the county is weighing in so long after the fact is just bizarre.'"
Tom Infield has much more in today's Philadelphia Inquirer (including a fresh quote from Mann, who now hedges his bets, if ever so slightly: ""I would think it is low probability, but it has been such a crazy case for years that it can't be ruled out").
Both stories also mention the latest plan by Congressman Jim Gerlach to block the move: "Meanwhile, Rep. Jim Gerlach, R-Pa., said Monday he has asked the Interior Department whether it is possible to designate the Barnes Foundation's Lower Merion campus a national historical landmark, even without the consent of the board. Such a designation would block the foundation from moving, he said." This is Gerlach's Plan B; Plan A was discussed here.