In order to alleviate an issue where some POS blocks were overriding already accepted POW blocks, a mandatory upgrade to v0.4.2 before block 420,000 was required.
sairon and an anonymous friend were able to fix the slow startup time issue with Yacoin-Qt.
Coin control feature was added to YACoin which enables users to control which addresses are used for their transactions and can help conserve coin age and privacy.
Due to the continuing wonders of open source software, another dev is able to continue where pocopoco and Windmaster left off.
Perhaps taking a queue from Satoshi, pocopoco "moves on to other things". Due to the wonders of open source software, another dev is able to continue where pocopoco left off and https://github.com/yacoin/ is born.
Original Yacoin developer pocopoco released Yacoin on 5/8/2013, introducing the following concepts to the world: