Regarding ICAO, though indeed it exists as an agency within the UN structure overall, and lacks the authority to enforce SARPs or Annexes or the Convention Articles as if it were a court of a sovereign state, IMHO the system it administers has enabled and supported standardization - not universally, but on a very widespread basis.
The suggestion by A0283 would seem to involve some change to Annex 13, such that a process for producing a substitute investigation report would be available. The lack of literal mandatory enforcement powers at ICAO does not make this a pointless effort.
Whether there is an informal, between-the-lines system within ICAO for imposing consequences if not sanctions as such, upon states which depart from Annex 13 processes (or other components of the ICAO system) is a "nice" question -- but its answer doesn't make the idea of a substitute report process - available after a certain lapse of time - an inadvisable idea.