Danske Bank (Denmark) recently lowered the threshold for negative interest rates to ~$16,000/€13,300, which is by no means a wealthy level. I wouldn't be surprised if other banks follow their example in the next 24 months.

EDIT: Source - https://www.nasdaq.com/articles/danske-bank-lowers-threshold-for-negative-interest-rates-on-deposits-2021-04-26

This is a change that would change a lot. In many european countries this gate would be very noticeable.
Development of the average private wealth per adult in Europe from 2000 to 2019
Source: https://statista.com/statistik/daten/studie/917215/umfrage/privatvermoegen-pro-erwachsenem-in-europa/

All ‘smart money’ is moving away from cash...

Exactly.
Why should you pay interest when you have it available yourself at any time and can send it globally?