It's not a taboo topic at all. Both Renderosity and 3DCommune have been looking into artists selling prints of their artwork, the problem here is getting a good deal for the artist AND the customer and guaranteeing that the end result is satisfactory and that shipping doesn't cripple sales because of increased costs. Selling electronic media images (computer file) is another thing altogether and unlikely to be accepted by the majority of customers who frequent this and other places. On that note though, there are several people here who have sold images through a RL gallery or from their websites so it does happen.