Eh. I'm more of the opinion that the price is set not by traders doing market cap calculations, but just based on the supply and demand on exchanges at any given point in time. So yeah, selling 1 million BTC via an exchange is going to move the price down, no matter how you structure it.
It's an interesting question how sentiment would react to Satoshi's stash moving. I think you're right it'd create a sell off, since it could make investors nervous. Not sure if this has any historical merit... one possibility would be to see whether the price has reacted in the past to bitcoin days destroyed:
Reveal spoiler
BTW, the data in that chart is from https://blockchain.info/charts, which no longer provides this chart (too bad). However, it looks like https://oxt.me/charts has a more up to date chart of BDD.