What is the probability that the reason for the non movement of Satoshi coins is that the private key has been lost ( and what implications does this have?)?
As wallets have become more secure would these coins not be moved to something considered "safer" ?
When was a large chunk last moved? If it was years ago does this not support the likelihood of a lost key and the inability to access these coins?
If there is proof/indication that these are still active/ accessible it would be nice to see that to put my mind at rest

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If there is no convincing proof of continued access then this article can be ignored.
http://www.coindesk.com/dangerous-satoshi-nakamoto/Satoshi certainly has a lot of funds. Bitcoin security consultant Sergio Lerner's oft-cited analysis puts the figure at around 1m BTC, based on the early mining that he or she did.
Most of those coins were unspent, the exceptions being some test transactions during the first ten days after Satoshi mined the genesis block (the first block on the blockchain).