From whoever was updating the L6 FaceBook page:
Some people might want to upgrade, other folks of course will choose not to. The new POD HD500x has more processing power, tour-grade construction, and new switches and lights for more confident use on stage. It is still a POD HD of course, so when we make updates to the POD HD, all POD HD owners will be able to take advantage of them. And our commitment to customer service doesn't change one bit.
It honestly sounds like they only upgraded hardware and put some LEDs in a beefed up chassis. Fortunately, firmware upgrades will be universal. Again, makes me wonder, did they just swap part bins for a better RAM/processor in their assembly process? Really hoping that's the case.