Rich Nesin, General Manager and Resident Philosopher, HomePNA, is claiming that G.hn (aka HomePNA Version 4) is soup--ready-to-go.
While the broken PHY specification was finally fixed in a recent meeting, they are still finalizing the MAC. Clearly the MAC will be "agreed" in June 2010 and equally clear expect a load of amendments and corrigendum in a years time to fix it as was done for the PHY. Review the ITU-T Study Group 15's history of the years efforts for them to make ADSL specification interoperable.
By-the-way, Rich does not mention G.hn's step child specification, G.cx (aka 9972). The idea of G.cx is to allow coexistence with other power line communication technologies. As HomePNA is a coax solution, this is not one of Rich's worries, but for G.hn to be success we need coexistence (as is in the IEEE 1901 standard).