This is an interesting idea. Given the additive properties of bitcoin keys it would even be pretty easy to make a key that was very very unlikely to be recoverable. Three people separately generate keys, throw away the private keys, and then mine to the product of the three public keys. It would take all three of them lying about throwing away the private keys and then collaborating to recover the combined private key to get the coins back.
Another possibility is that one (or more) of the 3 installs spyware on the other collaborators before the generation (or at least before the subsequent destruction) of the private keys. Then the attacker waits a while and then combines all the captured keys to produce the combined private key and claim/spend the mother lode.
I'd put this at pretty unlikely - I suspect the early experiment was never expected to take off anywhere close to what it has and so the foresight of doing this probably overlooked.
A great deal of effort must have gone into staying anonymous, and planning & designing & developing the client, the network, the scripting language, the economic progression (difficulty levels, decreasing block rewards, etc) and even the ascii content embedded in the genesis block. There must have been a plan for the first mining operation as well, why put in so much effort and then be surprised it catches on?
The "unfairness" of pre-mining (or early mining) must have been considered.
OTOH i haven't looked at the numbers. Would a dump of Satoshi's holdings crash the market?
I like this theory too. There was a lot of thought put into creating the platform, so it's reasonable to assume that Satoshi just opted to mine enough to bootstrap the network, and decided to throw away the keys in order to not be tempted to use.
Had Satoshi used the coins before its time, it could have "contaminated" the experiment, and possibly crashed permanently the market. By mining and not using it, it increased its early value. I'm sure there's a mathematical proof somewhere that this would be the best option, especially if Satoshi is in fact a group of people.
Of course, Satoshi may still have the keys, and waiting a bit more before cashing in.
That's the beauty of bitcoin open ledger: we'll all know for sure in the next 10-15 years...
They could probably still get wealthy by getting in on the action fairly early with a separate set of mining identities, if that's what they wanted.