Of the things mentioned so far,
* Full time single engine performance
* Problem free gearbox
* Camera to see the back of the helicopter
* Ability to fly in icing conditions
On the matter of the gearbox, it is not possible to simply over-engineer it?
helistudent- I don't mean to sound trite, but the reality is that all rotorcraft engineers put huge effort into making their designs highly reliable and "problem-free". I have worked with many of these engineers and I've never met one that would ignore an unsafe condition or sign-off on a design that had obvious problems. They all take their work very seriously and do the best they can. Every single part design has at least a dozen engineers from various disciplines (chief & project engineers, stress, dynamics, M&P, thermal, manufacturing, reliability, QA, etc.) review and sign-off on it.
As for the notion of "over-engineering" a gearbox to make it more reliable, I would simply point out that rotorcraft transmission components are already some of the most highly engineered parts in the world. They are designed and analyzed using the most advanced software tools, the highest quality materials are used, the manufacturing processes are very tightly controlled, and the entire design/manufacturing process is highly regulated by government agencies.
In reality, gearbox failures are rare. But when they do occur they can be catastrophic events. The reason is that there is only a single drive path from the engine input stage to the rotor, which can be disabled with certain types of failures. Normally this problem would be resolved by designing the aircraft with redundant and independent drivetrains and rotor systems, but this is not practical. If you or anyone else knows of a solution to this issue I'm sure the OEM's would love to hear about it.