The last info I see was from back in January when 4.1.2 was released for the Korean version of the phone. At this point, I wonder if the holdup is LG or the US carriers.
Personally, I see nothing I would die without that is in JB, but it bugs me to have what is one of the best phones on the market, and not be running the latest OS... Especially since Jelly Bean was released before the Optimus G.