That already exists. A will is most often in a sealed envelope, and you just need to add to it the keys to your wallet. Lawyers have been handling those kinds of things for decades.
But this is a different space. Do lawyer even know how to deal with bitcoin private keys? how do you know you can trust them? Has this ever been done before?
I would need to see how this actually went down in a real case, I just can't trust people including lawyers.