No Bitcoin is dead by definition - it may just be impossible to spend them, because e.g. you lost the private key. So you will never be able to distinguish between dead addresses and just untouched paper wallets.
I was also thinking about it and came up with a proposal for a protocol change: If it is well known and communicated through every news, and everybody would agree in that change of course, it would allow miners to 'take' money from transactions which are unspent more than (let's say) 2 years. This means they can transfer the coins to another address without providing the signature and the network accepts this. This sounds scary, but it wouldn't mean you steal somebody when everybody knows. You just have to move coins every two years. Unfortunately long-term paper wallets would be less convenient.
Of course details are missing, e.g. you shouldn't get all the money of a big transaction in one block just because you are lucky. Anyway, I think this "using of dead coins" idea wont make it, as everybody is interested in a rising bitcoin value, and this happens when some are lost!