Use web units to edit styles
Use pixel values for letter-spacing and line height rather than whatever Adobe uses right now so that it's easier to translate the specs to CSS
Use percentages or relative values to size objects and type.
eg: I want this object to be 50% of the artboard width
Add padding and margin pixel values to text to generate buttons. Similar to how you are able to create buttons out of text in illustrator (see: https://youtu.be/fiTnlCCXTBo?t=1m46s)
Great idea and really should be part of the "responsive features" that have been announced.