this can work. Colombia 🇨🇴 has a similar exit tax. Just a single $ number.
Logistically it creates its own problem with long lines waiting for the exit tax booth while people who forgot to save $$$ to leave try to figure out where to get the required cash (credit cards where not an option when I was last there)
that’s really nice. At Bangkok immigration I had to provide proof of 12 monthly installments from a foreign source for the previous year before they would let me switch out of the 800 K method