I don't know for sure how pension funds work in the US, because in my country it's a governmental organization that is responsible for all of the pensions. I guess in this country it's different, and you probably choose your fund (like a health insurance). What I am wondering about is whether people have their voice in that and whether the fund has any guarantees. Say person A has been paying a pension fund X for a couple of years now. This person expects certain amount of money back after retirement, right? So if suddenly the fund X decided to invest in Bitcoin, will the person X receive some guaranteed pension in the future or does it depend on the price of Bitcoin now?
I agree with bitfocus that it's better to have more stability in such important areas and not risk with money of an already vulnerable group.