These cases come up far more frequently than "one or two court cases" -- many takedowns of botnet/malware (e.g., Avalanche) end up in ROLR. See "domain generation algorithms".

In general, the vast majority of registries are fine with marking particular domains as "allocated but not delegated" as long as they get paid. ISTR ICANN waiving their fees, so the costs of marking a domain as undelegatable essentially turn in lost opportunity cost, which most registries are willing to eat.