Marion's contract is for $8.4 million in 2012-2013 and $9 million in 2013-2014 if he doesn't use his early termination option. It's not an albatross for a rebuilding team that doesn't expect to be a serious contender for a couple of years.
He's a better player than Joe Johnson for half the money.
With Dallas possibly wanting to clear cap space to make a run at Dwight Howard, if D12 doesn't want to come to Boston and you like Shawn Marion, it's possible a team with cap space could acquire Marion in the off-season for a deal similar to how the Lakers traded Lamar Odom.