It seems that DMarket provides additional monetization opportunity for game developers. Therefore all the rights for in-game items should rightfully belong to their owners - game developers. Smart contracts should allow transferring the items from player to player, reserving all the rights for the items for game studios.
These guys are already signing agreements with game developers to make this work. They've already shared that GSC Game World (Cossacs, S.T.A.L.K.E.R. and future new projects) and Tatem Games (Carnivores, Vivesector, Cryostasis) are supporting the project. Not the biggest fish so far, but they are in the crowd funding stage now and promised to announce more later. We'll see.
RE: How to trade and earn on in-game goods between ALL video games