Easy adding of breakpoints and adaptive views
If I design a screen for a special view (e.g. desktop 1200px), it should be easy to add new views (e.g. iPhone or iPad). All elements are copied to the new view and I can adjust them to the screen size. If you open it in the browser and resize the window, the right view is shown automatically, it must not be programmed to the window width like in JIM. See Axure - you don't have to work with masters and copy all masters to a new screen there. The rules for the breakpoints you set, when you create new views (see screenshot attached).
Since JIM has better responsive features (margins and width in %), this could bring it ahead of Axure for responsive/adaptive Prototyping.