I don't think its an good idea to have an bitcoin as a retirement account as the future of bitcoin is still blank. We don't know whether it will replace fiat or not but i would prefer to invest in some pension plans which would pay me assured amount of money monthly rather then going for bitcoin retirement account.
Pension plans are not good enough I guess. They don't pay a high rate of returns and you also have to pay the premium monthly or yearly depending upon the plan but If you hold good amount of bitcoin then it can proved to be a good investment option at the retiring age and you can sell bitcoins anytime you wish its not compulsory that you have to wait till you get retired
