I've given thought to this as well, some sort of multi-sig solution with a deadman switch where you can also provide your family with instructions.
There's absolutely no such need for a service for such a simple problem. How can you trust a centralized entity to give your Bitcoins to your family upon death, when you can't trust your family with your wallet?
It's completely useless, just ensure that they have access to your private keys.
No reason it can't be a dApp... and by your logic no one would write a will because everyone's family would already have free use of their stuff.
Right, but that's exactly what wills are for, and a will with the private keys
and instructions as to who gets what is all that's needed. There doesn't need to
be a service for this, which would probably be a scam anyway. If you write a will,
that's all you need to do.