Similar to the aforementioned Frank Mir fight, a bout between Andrei Arlovski and Josh Barnett would be a great nostalgia act.
Yes, Barnett is coming off a nasty KO loss to Travis Browne, but he is also ranked inside the top five of his division. There aren't a lot of viable options within the top 10 for Barnett to face in his next contest, so a pairing with Arlovski makes sense.
A Barnett-Arlovski fight provides both men with a winnable fight. Barnett's striking game is powerful but isn't the most technical thing to watch. However, his ground game is top notch.
Arlovski, meanwhile, has some of the best boxing—when he throws punches—in the division. He also has grappling credentials of his own.
Barnett and Arlovski shouldn't face any of the young up-and-coming heavyweights as their lack of athleticism would be a major hindrance. Instead, keeping the "senior circuit" going would be a good idea for both men and for the UFC's match-making people.