So the argument basically comes down to that crypto is too volatile and not usable as unit of account? 1. Crypto is still in its initial stage, where capital is flowing into it. Once it is there, it will be less volatile. You can already see this in Bitcoin[1], where relative volatility is dropping every year. 2. There are projects coming that will enable decentralized trustless peg of fiat currencies into blockchian…
Why do you want a long-term "store of value"?
Buy your grandchildren a pleasant mixture of diversified stocks and bonds---they and the economy will be better off.
Or, buy your grandchildren gold; it's had a much longer track record as a store of value and is prettier to look at while it is value-storing.