Could you make a multi-sig wallet with both keys required, give one key to a family member and leave the other in the will? Sure if no-one is capable of using them that's a problem, but I'm sure they could hire someone to do the retrieval.
I was thinking about this too, I gave my partner my passphrases and told her to look to the online communities to help her in the event of my death.
That would definitely work for wallets and individual coins. Great idea too. For me that only fixes half the problem. Being a trader, I have a large amount of crypto on multiple exchanges at any given time. That's part 2 of my dilemma.
Use decentralized exchanges as much as possible? I dont know if you can do multisig on Bitsquare for example, but it might be worth a try.