The volume would involve a crazy increase in the actual float, but the bigger issue is that everyone watching knows this is Satoshi, and any sudden move to sell would be a massive shock to the market because the current presumption is that those coins are off the market for the long term. If they are not, it changes a lot of calculations.

And assuming they have lots of other bitcoin to liquidate first, the reasons to liquidate the early coins are basically gone. If they believe the price will continue to rise, and have enough wealth from later coins, they'd have little reason to rock the boat.