Can't you just store your wallet seed on a set of flash drives or sd cards, along with the pc, mac and source tarballs for (say) electrum.org? You can also set up 2-of-2 and 2-of-3 wallets on electrum.
With google inactive account manager (for example), you can set up a dead-man's switch which will send these passwords, encrypted with an AES key that you have already shared with your designated heirs, in the event of your death or incapacitation.