Good differentiation from the heavy metal that is answering Nick's post. I don't mean to have a go at any light helicopter in particular but my (in)experience may show which I fly.
1. Can we please get rid of Magnetos? They are a pain to maintain and are such a dated technology that it is embarrassing to talk with auto engineers about them.
2. Ditto carburetors. The auto world also threw them out years ago. Carb icing still kills pilots and passengers every year.
3. Also can we have overhead cam engines that do not need two minutes run down time to cool the valve guides? I haven't needed a two minute rundown on my auto since my 1954 Jowett Javelin. (Pleasant twinge of nostalgia there, Mmm.)
4. Water cooled engines are generally quieter. I appreciate that at small scale they may be heavier.
5. Jet A1 is cheaper in many places, and diesel technology may give a 25% range increase.
Beyond Nicks allowed five points...
6. A service interval of 50 or 100 hours is indicative of a mechanical system working at its limit. If European auto manufacturers can give a 15,000 mile service interval (perhaps 300 hours at 50 mph...) can we at least look at increasing the service interval for new engine/airframes.
7. As Grainger pointed out, it should be impossible to overspeed the engine. An inexpensive rev limiter is fitted to many high performance auto engines and saves embarrasing rebuilds. (I once put a rod through the side of an auto engine at around 7500 rpm. Blame youthfull excess, but I then fitted a limiter.)
8. Fenestrons do scale down. They are quieter, safer in the amateur environment of light helicopters and are getting lighter.
9. Five point harness in the smallest of machines. OK with luck and skill I will never need it but I still feel more comfortable with them.
9. Despite several requests on the 'other' thread I do not need a cup holder. At my experience level I have yet to chew gum and fly.
For my two cents worth, I guess it all comes down to certification costs, but a diesel R44 would be a seriously competitive machine.