IPV6 vs IPV4 question is orthogonal to those addressed by the QUIC protocol. IP layer is for addressing nodes on the internet and routing packets to them in a stateless manner (more or less... I'm not counting routing table caches and such as "state"). TCP (and this QUIC protocol) are built on top of the IP layer to provide reliable end-to-end data transfers in some sort of session based mechanism.
I was thinking primarily of the security aspects, which is one of the few things called out. I'm all for secure and discrete transfers of data between endpoints, since TCP programming APIs often require maintaining process state for each connection and can impact service scaling.
If this is really more or a session layer protocol on top of UDP instead of its own transport protocol, then all the more power to them. It will be more of a programming model than a network configuration quagmire, and I'm sure that eventually intelligent optimizations can be performed via packet inspection if the protocol state details are not encapsulated deep within the security (i.e., trust/privacy) bubble of the protocol.
