i don't really think using bitcoin as a retirement account is the best option because the future of bitcoin is not certain as nobody really the future. Predictions is possible but it is not 100%. It could be profitable at the longrun or not profitable at all. Well, everything has risk, you just have to gauge the risk very well before taking the decision.
the future is not certain for any assets, and bitcoin at this point isn't any different, it could go wrong like it could go well, it is just a matter of perspective, and belef
if you really don't see any other better alternatives than using bitcoin as a retirement account, then go for it without thinking, otherwise you can sit on a more traditional method