So much depends on the pace of adoption and how far out you are from retirement. Someone posted a neat chart of this, but I can't find it now.

I think the figure for retiring relatively young, today, was in the tens of bitcoin. However, if you weren't planning on retiring for another 10 years, it was in the single digits.

I'm trying to workout something similar: What bitcoin income will I need to be able to quit fiat mining and make it until I can withdraw my retirement funds?