I'm not sure I would pick a number if I am honest, but I can understand that a number probably exists.

If this wasn't Thiel but rather someone else who made 60k/yr or 120k/yr, I don't think this would even be a conversation. So what if they turned their Roth IRA into 100 million.

In my opinion that is encouraging the right behavior and the intent. Investing 2,000 per year of their wages and trying to be somewhat forward thinking about their retirement.

Now there is the open question of if an average person is able to truly analyze such investments, but I think that is a separate issue as well.

I'm fine with limiting additional contributions to the Roth IRA once its value passes some number (and around $10M, indexed to CPI, feels reasonable).

I'm not bothered by investments whose value grows beyond that figure, to be honest, mostly because it's not clear what you'd actually do about it without trying to value unrealized positions and more likely compel transactions. (Valuing listed shares is relatively straightforward, but compelling transactions is abhorrent to me.)

I would go so far that additional gains above $10 million are exposed to capital gains, as contributions are inconsequential compared to the compounding of the account’s assets at that account value.

This is in line with QSBS tax treatment of corporation shares, where if certain conditions are met, there are no capital gains on the first $10 million.

https://www.brownadvisory.com/us/theadvisory/qsbs-tax-exempt...

Any balance in excess of ten million dollars at end-of-year should be a mandatory distribution. That’s a simple and very fair way to address the Romney-Thiel issue.

How about freedom and no limit? Why limit?