Can old coins be banned by a soft fork? Satoshi Nakamoto is supposed to own 1.000.000 bitcoins on a thousands of wallets, and most of them are untouched since early blocks. This stake can potentially flood the market, so miners could probably be interested in banning them. 

So, is it possible to create a soft fork (protocol update, approved by most of hashing power), that will deny any future transaction with early block coins? It is not really fair, but miners are greed and they should probably approve it. Is it a possible scenario?
Yes, since blacklisting a set of UTXOs would be done by adding more rules and thus restricting the set of allowed transactions, technically such a change could be introduced as a soft fork by the miners.

However, I would sincerely doubt that censoring Satoshi from spending her coins would find broad community support. I suspect that such an endeavour would quickly escalate the already existing tensions between community and miners.