I wouldn’t expect ATSB to do further investigative work across a variety of types, and would not criticise ATSB for not doing so. The ‘normal’ exposure to CO from the ‘normal’ operation of ‘average’ GA aircraft is evidently not a safety issue.
However, cracked exhausts and other defects will create CO risks in any GA aircraft. The questions in the case of this tragedy include:
1. Why were the defects in the engine bay not detected during any of the required inspections?
2. Why don’t the mandatory equipment requirements for a ‘standard’ GA aircraft require a reliable CO detector (and engine monitor) rather than pointless crap (from a safety perspective) like ADSB?