That was really interesting. Also watched the video you linked to, which he did a very good job with.
A few things I wanted to note:
1. Box 3 is an income tax, that can function as a de facto wealth tax. If you do not provide proof of actual income from certain assets, they assume a deemed/fictive income of 4%, based upon the overall value of those assets, and charge 36% income tax on that. This tax has been in place since 2001, and the project to reform Box 3 was begun in 2024 due to a Supreme Court case triggering gigantic tax refunds.
2. They were planning a move from the deemed/fictive asset-income tax from 2001 to an accrued gains tax in 2008. He says that the new government is in deliberations to change this proposed accrued gains tax into a capital gains tax (i.e., move everything to Box 2). That means the government is trending _away_ from an existing wealth tax, rather than toward a new one. I don't think you made that clear.
3. You suggested that this would hit the middle class hardest, but they don't pay this tax. Labor income (employment, businesses, and wages) and personal homes are exempt, and there is an €59,357/person exemption on owned assets. That does not mean that the vast majority of residents are paying a lower tax rate, as they are being spared this tax. They are paying a much _higher_ tax rate (up to 49.5%). The overall tax burden in the Netherlands is probably simply too high, overall. And people who own at least 5% of a listed company are in Box 2, not Box 3.
4. The people who would struggle the most, with this new tax, are startups, but they have already been given an exemption, and that exemption is to be expanded further, to cover any "innovative" company. Which is basically everyone. (As per usual, the lobbies have created so many exemptions and loopholes that the tax is pointless, which is why it will probably be scrapped and switched to Box 2.)