The idea of adding things to the marketplace which is funded only by people spending money on that same marketplace is good. Part of the income going to other in-game things is good too.
What may be a good option, is to add those marketplace items into the game half a year later or so with different ways to get them. Perhaps with the textures in a different color.
People still have the incentive to buy it in the marketplace (to get it a lot sooner), while anyone can eventually get it.