What about this, you print your wallet.dat and store it, and print the method of reading it
30 years down the line (BTC is still around) your kids find it, and wish to decode it,
Paper last longer then most digital medium at the moment
Agreed. Very cool.
edit---
So in 30 years people have to still be able to run this program or could it still be decrypted as long as the passphrase is known?