Hue is currently stateful because in IMPALA-564, Impala will close the session if the connection is closed. Among other things, this prevents us from stateless load balancing because we need to route users to the same Hue backend that holds open the Impala socket.
According to the HiveServer2 design document, the HS2 protocol allows for the session to independent from the connection. Adding supporting this might not be too difficult. The connection is explicitly closed here, and it's possible removing this block for HS2 connections might be sufficient to enable this feature.