It looks like Epic Games is a private company, so from what I understand in the proposal, this wouldn't affect him, since his shares are not publicly tradable. The proposal might affect him when/if he were to sell any shares, though, since it has a provision to accrue tax liability on illiquid assets like art/etc, to be owed at time of sale.
From what seems to be the intention of the tax plan it would be regardless of if the asset was available in a stock exchange so if the value of Tim's shares put him above the threshold he would still have to pay the tax. His wealth through epic would likely be less then if it were a publicly traded company though. The effect of paying tax on shares was always true as it becomes a realized capital gain and is already covered under the current tax system.
The stories I see, like https://www.cnbc.com/2021/10/25/senate-democrats-push-for-bi..., says the tax on unrealized gains only applies to "tradeable assets." It doesn't seem like that would cover private companies. From what that article says, it would invoke an increased tax due to the deferral of taxes though.
It still seems problematic. Even if my company goes public, if I haven't actually sold the shares and made any money, why should this be taxed? If there are loopholes that let the founder avoid those taxes at sale time, fix those, but otherwise why should we effectively take away ownership of a company just because someone has built it up successfully.
One loophole is the step-up basis that applies when the owner dies. Not sure why that wasn't targeted instead (maybe because the current plan produces revenue more quickly?).
