I think there some disadvantages in having a retirement account with bitcoin because we dont know what will happen to bitcoin in the future will it lasts forever or stay but its good also having a retirement account it will make bitcoin more active.
WELL I think if we hold a good amount of bitcoin in our wallet then this will surely be the best option to have a retirements account, because any that you have to surely get fade someday and you will have to get retired from but I think bitcoin will raise more and more in future and holding good amount of bitcoin will make your retirement life safe and secure,. So having bitcoin is best option, as it is the most promising investment.