It'll only be impossible to hold for long periods of time. We can start the tax at $1, it hits $1mil after 20 years - and for 99.9999% of IP by year 20 it's either clearly worth zero or clearly worth >$1mil so it'll be an easy choice. It'll force things into the public domain faster and make it expensive to hold a big bullshit patent catalog, but for actively used properties it'll be fine.

Companies are going to want to sell in one of the richest markets in the world; they can either pay for IP protection or not be granted it.

edit: I'm not suggesting these exact $ values as clearly being the correct ones, it's just an example.