First I am not in favour of the wording Oversight Council or any such attempts of councils and new orgs etc.In the IANA sense of things, I'd stick with an ad-hoc committee that would be put together with representation beyond a registry controlled group. This committee can be well equipped to deal with SLA and contractual agreements etc.
Such a committee must be established on the basis of a multistakeholder representation that is renewed each year in an open and transparent manner where openess, diversity, inclusiveness and the user perspective is well represented.
Whoever says this is impractical may be over looking the fact that there is similarity with IGF MAG and various ICANN AC/OC selection processes though not optimal but indeed adoptable with certain improvements.
Making IANA prone to new councils or orgs etc is impractical. IANA can itself exist independently with an Advisory or Management committee with rotating yearly membership but contractual staffing.
BestFound