I don't understand quantitative finance, but I had the impression portfolio theory can find a place for any amount of volatility. If the volatility is very great or it's correlated with the rest of your portfolio, then your appetite may be small, but high returns may make it still worth buying some. Is that wrong? I also have the impression that bitcoin's volatility has been relatively uncorrelated with other asset classes, so that'd be a plus. (Maybe I'm wrong about that too.)