> So even if I store my wealth in cash, you want it to deflate by 5% annually?

Generally speaking, that's the point. The wealth tax is trying to combat wealth inequality and the only way for such a policy to be effective is if those with considerable assets wealth decreases with time.

> How do you handle your neighbor who discovers he has a $2m Pokémon card in his closet?

Usually that's handled by having a minimum asset requirement before the wealth tax kicks in. 100M is what I've seen. It'd be a pretty easy tax to make progressive.

> It’s a messy proposition. I’ve yet to hear a clear proposal that doesn’t have sticky edge cases.

I've given the proposal I've seen in a different comment. Perhaps you didn't see it? But in any case, taxes are always messy. It's not as if you can't refine them with more and more amendments to address different scenarios as they come up. I don't think the "messiness" should be what keeps us from adopting such a tax system. There will almost certainly be a game of cat and mouse between the regulators and the wealthy regardless the proposal.

Don't let perfect be the enemy of the good.