I've done a tiny bit of research on this topic, but haven't found a clear answer, so I thought I'd post it here. It's a bit complicated of a question, but I think it's super interesting to work on an answer.
Let's say you're a U.S. Citizen who retires at 35 or 40 with a $2 million dollar portfolio. For this example, half the money is in taxable accounts, half is in non-taxable.
You decide that you no longer need to live in the U.S., and you want to spend become a citizen of a more favorable tax treatment nation like Belize, Cayman Islands, Etc...
You renounce your U.S. citizenship.
What kind of tax would you owe? I've read a little bit of the IRS publication here:
https://www.irs.gov/individuals/international-taxpayers/expatriation-taxAlso,
If you knew in advance at the start of your career in the US that you would eventually renounce your US citizenship, would you put more money in taxable accounts vs. IRA's or 401K's?
Obviously you would forfeit your SS checks in the future, but for early retirees that wouldn't be too big of an issue.