No one knows who Satoshi Nakamoto is, if he's alive, and whether he will use his bitcoin in the future. He could move the market if he chooses. At one point he was an oligarch, correct? He had money and political power as far as Bitcoin is concerned.
i dont believe the spending of Satoshi's (nor anybody else's coins) would cause any issue, since the market knows of the existence of these coins. It's that bitcoin is quite volatile due to its immaturity as a currency and commodity (it seems to act as both atm...)
Unless satoshi has somehow hidden a large chunk of coins that has never been released somehow (which, would be weird, since as soon as they release it, it would invalidate the current chain!)