The common theme behind the avoidance mechanisms is "keeping the gain unrealized." Going after preferential treatment of unrealized gains categorically attacks every single one of these tricks. It nukes the hydra rather than trying to chop off heads one at a time.
I am of course deeply sympathetic to the "founder scenario," but I'd rather address it specifically than hobble tax collection generally. This could be done by a "payment in-kind" mechanism. If we wanted to steer it towards startups I'm sure the valuation rules could be set to do so, but I'd personally like to aim higher and go for progressive taxation on the basis of market cap to encourage company splitting and competition. Industries with the most dramatic returns-to-scale (semiconductors) could be exempted.
That said, the (in)ability for new founders to self-fund is deeply tied to the same gini coefficient story as the rest of the economy, so policy that addresses the gini story should help bootstrappers as well.
> Going after preferential treatment of unrealized gains categorically attacks every single one of these tricks. It nukes the hydra rather than trying to chop off heads one at a time.
Now think about how they're going to respond to it.
A major problem with taxing unrealized gains is how to measure them. For publicly traded companies that's pretty easy -- the stock is undergoing regular market transactions so you have a pretty good idea about the price. But what about assets that aren't? Closely held private companies that aren't listed on an exchange and haven't undergone any stock transactions in ten years. Art. The value -- or liability -- of a private contract for the future sale of goods at a defined price, when the market value of those goods might have since changed, or depending on what they are, be indeterminate.
It creates endless opportunities for playing games, and that complexity is exactly what allows the people who can afford fancy accountants to pay less in tax than everybody else. If you want to fix it you need to make the system simpler rather than even more complicated.