Here are a couple of interesting tidbits:
It's continuous power
It's at a minimum for only the main L and R channels
It's at 1% THD+N to accommodate tube amps that can't hit the originally proposed 0.1% limit
It doesn't say anything about the rest of the channels of a multi-channel amp
It has to be at least 77 degrees, so you can't test an amp at low temperatures when it cannot put out the power at higher temperatures.
They received lots of informal comments but only a dozen or fewer "formal responses" to the proposed changes over the last four years they have been considering it.