I first saw it on a project called BitWasp. It was an attempt to make a SR like marketplace with open source software, the project was never finished.
Kudos to the BitWasp devs.
I strongly believe that software can be made to allow any vendor to set up their own site. Each site can export datafiles containing inventory, payment addresses, and feedback. By using PGP signatures these files can be published and imported by other markets. This would allow the creation a truly federated and interactive marketplaces.
If you used the same PGP key to login to marketplace A as you did for marketplace B then market B can read the signed feedback from market A and import it for you.
If you were on my market which sold LSD and MDMA I could also list DMT from another vendor who I trust I could just import their inventory file complete with payment addresses. I would then send him the order file in exchange for a commission.
Sites with no products of their own could import many people's data files has host their products for them, removing the need for a vendor to manage their own site.
Escrow could be decentralized too with a similar system or the federated feedback system could allow trust relationships.
There are nothing tecnilogically new in these ideas, the just need to be implemented and implemented well.