>That's just price control, which always works great in market systems.
It's not a price control. Price controls are like minimum wage laws which regulate the price at which market participants can sell goods and services, and are generally broken because they lead to a shortage or surplus (depending on whether the price control is set higher or lower than the would-be market price).
This is effectively a tax. Taxes are an extremely effective method of behavior modification. Their primary economic consequence is to discourage the taxed activity, which is undesirable in the case of e.g. employment, but in this case is exactly the desired outcome.
>If you did that, squatters would just lease out domains instead of selling.
Are you serious? Nobody is going to lease a domain name, because the minute the lease expires after you've put all your marketing efforts into telling everyone what "your" domain name is and having them use it, the squatter could just raise the price by a factor of a thousand and have you by the short hairs. And a lease that allows perpetual renewals should be considered a constructive sale for the purposes of the fee and require immediate payment.
>Or you know, take this gift of bitcoin in thanks for free transfer to me.
That would be fraud and could be subjected to criminal penalties. Also, the fee would apply to the seller, so the non-repeat purchasers just buy the domain name pursuant to whatever covert payment method the seller is using and then report the squatter to the authorities which costs the squatter the $20,000 plus penalties and gives the buyer the satisfaction of sticking it to the jerks who were squatting on the domain they wanted.