I will honor all of this with by reading it.

Just for a first response to your second paragraph

Let’s say the stock does really well over the next 10 years, and it doubles in value, 100 at a time - at some point I (as an investor) will have paid 25% of that, so I’m virtually paying 1250 for that $2000. Cool, that’s what would’ve happened if I had sold.

You will have "paid" $250 after the ten years, not $1250. So if the stock tanks, as it can with the current system, nothing would change. The point though is, that you have not actually paid that $250 out of your pocket, the stock has just gone up by a total of 1000-250 instead of the whole 1000.

So in my eyes, the risk for you is exactly the same as it is now. You still gain $750 over 10 years, and the government still gets its $250 in taxes.

-- I will read the rest of your reply now, that's just my first thought. Thanks for taking your time to think this all through :)

Second thought: Yes, I think I get what you are trying to say.

• If the stock price rises in year 1, after the yearly tax cutoff it will have paid taxes. 1000 + 50 * 75% = 1037.50 [1050 with the current system]
• The stock tanks in year 2, losing 50% of its value, and ends at 518.75. There would be no taxes owed, because losses > profit. [525 with the current system]
• In year 3, the stock rises again, by 100% this time. Would end at 1037.50, but after the tax cutoff ends at 907.8125 [1050 with the current system]
• You decide to sell. With the new system, you get exactly 907.8125, as you already "paid" your tax. With the current system you get 1050-(1050-1000)*25% = 1037.50

-- this means the new system would have to do something during loss-years. yes, I see that now

Third thought: This makes me feel like there should be a loss-counter that could be carried over the years. This counter would have to be held for every single share, so that you would start "paying taxes" or lowering the stock price again only after you were at +- 0 again.