How would you implement that in startup world for example?
It's very common for startups to be valued at ~20M$ right out of the gate in seed stage, not because the company is worth $20M, but because at $20M valuation it allows the VCs to invest say $4M and only take 20%, no one want the VCs to take more (not even the VCs themselves) because otherwise it would mean the founders are left with too little equity too soon and probably won't care about their business anymore.
Now, as one of the founder, maybe you own ~40% of that business, so now your paper net worth is $8M, and just made $8M of unrealized gains in that year, how are you going to pay that?
There is no way you will ever find someone to buy $1M of your share at the price of that round, you probably wouldn't find anyone willing to buy your entire paper $8M for $1M, because again, the company isn't worth $20M yet.
This is true until pretty late in a VC backed company, most round aren't priced based on how a realistic buyer would value the company, they are priced based on complex dynamics. Even a large number of unicorn startups founders in the Series C/D stages would have paper wealth of potentially 500M range, but absolutely no way to find 50M.
So, you effectively have no way to pay that tax.
This system actually already pseudo-exist in Canada in specific conditions: If you stop being a tax resident of the country, all your assets are considered realized the year you leave and you must pay taxes on them. Which is effectively impossible for most startup founders, because again, your stock isn't actually liquid. This means you can't stop being a tax resident of Canada until your companies either dies or you exit somehow. To be clear you can't easily just choose to remain tax resident of Canada while living abroad, Canada gets to decide, to maximize your chance you must prove that you still have ties, so e.g. you have to keep a home, you have to keep your bank accounts opened there, you must visit often enough etc.
Canada revenue agency offers one alternative: You leave the country but leave your stock in their keep, on the day you actually realize the gains, they will take what they were owed, which sounds great, except if the company fails, or you realize gains at a lower valuation, they still consider you owe them what was computed the year you left, not the day you exit, so there is a real risk of being in debt for the rest of your life.
Minimum thresholds, and exceptions for less liquid assets (private equity) - ideally, again, coupled with thresholds.
The same way we have exceptions like CA Prop 13 for increasing property taxes.
These problems aren't impossible to solve. It's wild how people will find any tiny excuse to give up on making a change to try and make tax code more fair. If there are edge cases that a blanked change to the code makes worse, that's NOT a reason to just throw our hands up and say "whelp, can't make changes" - it just means we need to add a bit more nuance.
You set a minimum threshold to trigger it, and you set certain realistic exemptions for things that would benefit society, including giving a VC time to mature.
Now, as one of the founder, maybe you own ~40% of that business, so now your paper net worth is $8M, and just made $8M of unrealized gains in that year, how are you going to pay that? There is no way you will ever find someone to buy $1M of your share at the price of that round, you probably wouldn't find anyone willing to buy your entire paper $8M for $1M, because again, the company isn't worth $20M yet.
This is true until pretty late in a VC backed company, most round aren't priced based on how a realistic buyer would value the company, they are priced based on complex dynamics. Even a large number of unicorn startups founders in the Series C/D stages would have paper wealth of potentially 500M range, but absolutely no way to find 50M.
So, you effectively have no way to pay that tax.
This system actually already pseudo-exist in Canada in specific conditions: If you stop being a tax resident of the country, all your assets are considered realized the year you leave and you must pay taxes on them. Which is effectively impossible for most startup founders, because again, your stock isn't actually liquid. This means you can't stop being a tax resident of Canada until your companies either dies or you exit somehow. To be clear you can't easily just choose to remain tax resident of Canada while living abroad, Canada gets to decide, to maximize your chance you must prove that you still have ties, so e.g. you have to keep a home, you have to keep your bank accounts opened there, you must visit often enough etc.
Canada revenue agency offers one alternative: You leave the country but leave your stock in their keep, on the day you actually realize the gains, they will take what they were owed, which sounds great, except if the company fails, or you realize gains at a lower valuation, they still consider you owe them what was computed the year you left, not the day you exit, so there is a real risk of being in debt for the rest of your life.