I love to see this list, because it means Scirra knows exactly what areas I think they should be focusing on.
Debugger is a must - I hand rolled my own quazi debug window, but a native solution would take the framework to the next level, it should be a priority before pretty much anything else.
Modularity is key as well, any improvement in this area will be big for construct users and depending on how it's done could really help people working in small teams.