I don't think YAC needs a marketplace right now, as I don't think there is enough people to support it. What YAC needs ATM is :

• A community driven place, a place where people can find the software and documentation (AFAIK the yacoin.org is not updated anymore and run by someone that has nothing to do with the original developer)
• Active development .
• A public GPU miner (otherwise the network is always at risk).