Infinitely many "domains" for a finite price. I guess there is no icann fee etc, all sales will be pure profit minus management costs (which costs?).
Porkbun and epik don't sell .s yet.
How many registrars are participating. I mean, if it is a small number, another group of registrars could form another group and introduce their version of the same tld.
icann and hns people need to make a deal to make sure their tlds don't overlap. otherwise either hns would lose, or hns would create its own .com. Or icann or donuts could buy a handshake domain and turn it into dns domain.