We used to have something like that, share.krita.org and integration in the application itself through GHNS (Get Hot New Stuff) – a KDE framework. However, we couldn’t manage share.krita.org because we’re too small and busy a team and because of the way that site was set up by the owners. So it became a huge spam magnet.
I really want to have a dynamic marketplace site where people can actually sell their resources, with integration with the new front page Sharaf is creating at the moment.
But that’s not going to happen overnight.