I think adding a hard mode is a cool idea! I wouldn’t want to just add more tasks or make Cobb faster though. Maybe new rules or even a second monster that has it’s own ruleset could spice it up and make it feel different from normal mode.
Also, your “Option 2” is pretty much what endless mode does, except the map gets increasingly larger and Cobb can duplicate more and more times. It gets pretty brutal, sounds like you’d enjoy it. (My best on endless is level 9, good luck beating that!)