Actually, if it's limited to those with over a million in "wealth", it'll only be a serious problem for the Wall Street types. Because 20k in straight cash isn't that hard to have extra for the upper-middle-class who have a million in property, because such people generally have well over 100k income. It's a blow to disposable income, but it isn't a blow to holding onto wealth.
At 2% and needing over a million in valued owned property, only the "renteer" class of people who's income is based on making people pay them for shit they have nothing to do with building are getting fucked outright. Real estate moguls, stock holders, you get the idea. Pad it out more to the ten-million threshold, and it'll be genuinely certain that it's damaging to the upper class, but basically harmless to what middle class we have left.
Except you're leaving off an entire class of people in this analysis: small and medium business owners. The ones who actually make a huge amount of the jobs and represent the most real and local economic growth. A person who owns a decently successful restaurant likely has well over a million dollars in "wealth" (assets) to their name, but they're also probably only making a middle class living on said wealth and income, and thus likely CANNOT afford to pay $20k more in taxes per year.
This is doubly true if you happen to be a business owner in a high cost area, where a large amount of your wealth is tied up in real estate and thus is not liquid. I mean, consider this, a middle class home in the DC suburbs can easily go for $300 - $400k. Now assume they own a storefront in a decent location, which is another piece of property in the $300 - >$1 million range depending, but take say, this
property in the DC suburb of Manassas which is for sale at $485,000. So for this we'll go with $400k and a house at $300k. That's $700k in "wealth" already,
none of it liquid. This is not counting all the goods in the store they own, which are also considered assets and stop and think about just how much money in goods is on the typical convenience store shelves. Yes, the amount they spend on it is less than the amount they charge you for it, but even so, it's still likely hundreds of thousands of dollars worth in yet more... non-liquid assets, but things that still count as wealth. It would be ridiculously easy for a small business in the right location to qualify for this tax, yet the people be unable to pay simply due to real estate costs.
What does this then amount to? Those small businesses, the Mom and Pop shops and stores... they cannot afford to pay the taxes, all their "wealth" is tied up in the business and the money they live on is likely more akin to the standard middle class or, if they are very successful, upper middle class lifestyle of the region. The typically middle class family CANNOT absorb an additional $20k minimum in taxes, and thus they will be forced to close and sell off their business. You know who CAN afford to absorb those taxes? Big corporate chains.
Thus all a wealth tax REALLY does favor big corporations and grant them further power over small local businesses. Like most government market regulation tends to.