Not sure why you have chosen .500 as your benchmark here, but if anything, .625 (10-6) should be the line in the sand if the NFL were to institute one. Still, I think it's a lame idea because the owners have all agreed to this and they were the ones who also agreed to the current divisional alignment. Some knew they were in weak divisions, some knew they were in powerhouse divisions. Suck it up and deal with it.
I would root like hell for a sub-.500 team. Man that would be great to watch a team $20M under the cap sneak in and run the table.