Selling citizenship didn't work out so well for the Romans.
Your thinking is in term of political influence? And more money related political influence? In some ways that's already on us with Soros and Musk. But you bring up a good point, but as long as we restrict these newly minted citizens to just money, and not becoming legislators or Presidents, I think the good outweighs the bad.
Just running some rough numbers here.....
5000 cards @ $5M each. = 25B seed money revenue to the treasury coffers
Say each card owner is a Billionaire, or averages a billion net worth, - And sees personal and business income at $100M ea. That means a perpetual tax stream of about ($20M x 5000 citizens) of a $1B per year
Then add trickle down business ventures.... And those incomes, and tax payments... etc.
There are other countries that do just this with less bravado, like Australia. I just see this is a innovative way of many we can do to chisel down the debt.