This is a well questioned path on this forum. To operate single-engined over "hostile" terrain requires a number of mitigations to be in place to reduce the risk in the event of an engine failure. Commercial or Military operators are very familiar with these, and again I would be fascinated in the data that shows an engine failure (or drive issue) at altitude that can't be managed with a correctly executed autorotation, including zero speed onto rugged terrain. The main risk mitigation for non-commercial operations should be not to operate over "hostile" terrain unless absolutely imperative
Hence my quotation marks around the word hostile. Although operations by professoinals over hostile areas must be mitigated and engine failures are rare, we see SE helicopters flying at night on EMS missions over built up areas, I often see smaller private helicopters being flown with low regard for where they might land if it all goes quiet. Add the potential difficulty of achieving a successful autorotation and EOL in the heat of the moment for many leisure pilots then is a great idea worth developing.