Ran across this site put up to flip .co's....nothing listed yet.
Flipping .CO domain names
I got 2 of the 3 I pre-registered today Going to develop one, the other probably put up a lengthy article on the niche the name relates to, link build, and see how it ranks after 2 mos or so. If .co's start selling, would likely list it for sale.
If you sell, please let us know how it goes and I'll do the same!