I remember reading about our national/provincial archives discussing archival of personal data. The provincial archives already accept (historically interesting) documents from deceased individual people, so they were thinking of extending that to electronic documents too. Don't know what the actual current status of that project is. Digging a little bit in the archives website, they seem to accept material on mutually agreeable basis, subject to resource limitations, and expect the donator to do appropriate footwork to help to make the archives usable - so it'd require extra work from the inheritors and it's not exactly "came to drop here the old man's hard drive, kthxbye".

And there's several more specialised archives, especially what comes to art and photography and other special interests.

So I guess putting PINs and master passwords in the wills is just the first step. The second step would be to encourage your inheritors to work with the professional archivists. Or, heck, become professional archivists. Setting up and curating private collections can be fun.