I very strongly believe you to be wrong:
1. Unrealized gains is unworkable. Billionaires will spend tens or hundreds of millions yearly to avoid paying literally billions in taxes because the expected value is net positive. The IRS won't win chasing down money scattered across the globe. This is not a productive use of capital.
2. Taxing unrealized gains causes extreme capital flight. This is _bad_ for the US.
3. Taxing unrealized gains will lead to corporations and startups incorporating outside the US and keeping their assets outside of the US. This is _bad_ for the US.
4. Founders would very quickly loose control of the companies they started, including before they exit. That is really bad for startups and the ecosystem.
5. This is almost certainly illegal in the US at the federal level.
6. Every tax for the wealthy eventually targets the middle class.
It specifically states that this only applies to individuals with 80% of their wealth in tradeable assets. No founder is going to lose control because this doesn’t apply to them!