6. Fully customizable colour.
(I hear various instruments in specific colours and I want very much to match what I see to what I hear. It would make my work so much easier - I'd be able to make appropriately coloured templates and pick out various instrument tracks and groups at a glance.
I know that, to many people, colourizing seems frivolous and is scoffed at as an exercise in trivial decoration especially when compared to "serious hard-core engineering" features. To some people, though (including me), it's the difference between an intuitive, fulfilling, rewarding experience and a somewhat frustrating, dry and tiring one.)