Every month, your employer transfers Bitcoins into a time-locked address that can't be transferred out before you reach retirement age. You have the key to the address. You can verify the transfer on the blockchain.
No middle-men. No funny business. No brokers with pyramid/eyeball shaped logos. No "oops we went bankrupt and lost your retirement." No bail-ins. No raising the age of retirement.
Just Bitcoin.
That can be considered mate, but since you're talking about retirement here, I just think that it's just too risky to consider it as a retirement fund knowing that anything can happen to it for better or worse. I say that because it's just too uncomfortable to rely on something that can change value at any point, more so lose it's value altogether, especially considering that one would use it as funds to sustain themselves after working. I would rather have some in cryptocurrency but more as money stashed in a bank.