Wouldn't they figure out a way to split their holdings into smaller delegate trusts, something like that, to come under the threshold?

That's certainly a concern, but the IRS works for us so if we choose for them to investigate tax evasion by the wealthy they should do that.

You think the IRS works for us... that's cute.

Unless you are a large corporation / billionaire yourself, in which case I apologize, yes it works for you.

Well, obviously, I don't actually think that. USA as a system of representative government, if it ever actually existed, certainly doesn't exist now. There is no way for the polity as it exists to stop taking everything from the majority of citizens and giving it to the authoritarian rich. The eventual answer will be a breakup, with the wealthy Pacific states escaping first and various other regional subdivisions giving up on the dream until finally the DC vampires will have no more victims left. Some of these successors to USA will reproduce the same broken system, only at a mercifully smaller scale. Others, I hope, will reduce the harms that arbitrary authority inflicts on humanity. Since we'll all still be Americans, many of us will be able to move to e.g. western Iowa if they figure out the best way to live before the rest of us do. At least once bond-holders are no longer tempted to finance our horrible wars we won't menace the rest of the world with so many of them.

However, when discussing the various symptoms of this fundamental malady, as we are ITT, it's often useful to take the marketing at its word. It would be nice if our IRS were created and operated in the interests of justice for the vast majority of Americans. Let's imagine how that might be, and see how far the actual falls short of the ideal. The quicker we see USA as it is rather than how it has been sold to us from birth, the quicker we'll figure out something else marginally less awful.

it's easy to talk about how much other people should pay. why shouldn't you pay a regular tax on your assets?

Yes that's what we're discussing ITT.

There are any number of principled reasons to oppose paying taxes to USA government, but "I'm rich and I can afford the lobbyists and tax attorneys to make the system work for me" is not among those.

The entire middle class already does pay a regular tax on their assets. We call it "property taxes". The groups who AREN'T taxed on the bulk of their assets are the poor (who have no assets) and the wealthy (whose assets aren't taxed).