If you’re sure you can make $100m on your idea, it should be easy to find an investor to give you $2m. If you can’t find an investor to give you that much, maybe your idea is riskier than you thought and therefore not actually worth that much.
The original idea for this tax structure is for land. Namely, a piece of land can only be used for a limited set of purposes at a time.
As a society, we want land put to valuable use. We don't want a piece of super valuable land (could be producing food, etc) that is dormant simply because someone refuses to sell.
But we also don't want to be the arbiter of what counts as valuable. So you state the value of the land and pay the tax on that value. If someone else can extract more value, they can buy it from you at the stated price.
I think this sort of tax makes less sense for intellectual property, because unlike land many people can use the same idea at once.
The reason I like it for IP is that the cost to society to enforce IP rights is pretty high.
Not just directly (e.g. costs to grant patents, hear court cases etc.) but indirectly - people can make things completely on their own and end up being sued for it because of an obscure patent violation. This has a chilling effect on innovation in general.
Because of this, making the person with the special right have to pay for the costs of that right seems fair.