I found this very interesting
link on bicycle chain efficiency.
A study found that the first factor in efficiency was cog size (larger is better), and the second factor was tension (tighter is better). My thought is - maybe you don't need to worry about chain slipping issues if the tension is tight enough? (Not on the dérailleurs though.)
Every little bit helps with lowering the wattage required for a given speed. The idea is if you can minimize the wattage it takes to cycle at 60kph (compatible with most city areas), and if you can take care of acceleration issues with electric assist/regen etc, then you have a commuting vehicle that will keep pace with city traffic and hence be more convenient and less dangerous.