There is indeed "inheritance problem" and there are many solutions. You can mix and match solutions to best suit your needs. Now let's see what lego pieces we have here:
1. wallet.dat + the the rest of software i.e. bitcoin client, OS, encryption/description software plus expalnation notes/documentation + storage
2. "dead man" switch
1. wallet.dat + the the rest of software i.e. bitcoin client, OS, encryption/description software plus expalnation notes/documentation
Do not just pass wallet.dat, make sure that there is a complete suite of software and documentation is passed along it, preferably including bitcoin software and OS in a self contained and self sufficient package. Bootable USB stick sounds as a good idea. Note that lifetime of such sticks is limited 5-10 years maybe. Burn also image of such USB to a CD-R and/or DVD-R. On a plus side this allows one to use a linux distro which includes encrypted partitions. This gives a decently secure and reliable way to pass wallet.dat. Ultimately, one can get low cost netbook, put everything there and store it securely. Than all you have to do is to pass access to such netbook along with the password and instructions/docs. There are many ways to do this step, chose what you think is the best for your circumstances.
See how we have simplified the problem now. Many copies of such netbook/USB/DVD-R encrypted are distributed using variety of methods the only problem left is to give your heirs a password message securely after the event. Here comes "dead man" switch
2. "dead man" switch
There are a few options. Check out https://www.deathswitch.com/ . Wills, lawyers, separate safe deposit boxes etc... You even could tell your child "I love you my sunny pumpkin" every evening when they go to bed and than say in "will" remember 6 words I told you every time you go to bed... this plus '34534dfgdskjhagdsgvsdfk3p98ulkjKhsdkfvskdfhblsdhbf' is the pass phrase, no spaces. Mix and match
Conclusion
Once we have separated the problem into 2 parts "encrypted data" and password, things get easier. Mix and match as you see fit. Keep things encrypted and documented. Keep password separate. Make sure your heirs get access to all pieces of the puzzle after you dead. Make sure nobody gets access to all pieces before the event.
Also consider inheritance taxes and how you want to get around those if at all. There are plenty if instruments like trusts etc... and if it done right it's a good thing. Considering that a few bitcoins might buy a mansion some day it probably worth taking professional advise on this matter.