Distance of at least 80 miles, course laid out with a mixture of flats and tough climbing. All riders required to use their regular mass-start road bikes and no aero equipment.
The idea is to simulate a long solo break. That's the reason for no aero equipment. 80 miles gives you enough distance that you can work in an interesting mix of climbing and flats. It also is long enough that riders have to carefully manage their power output. Can't just run at LT until you drop.
If you got the mix of climbing and flats right, neither the pure climbers nor the TT specialists would dominate the stage, and it would give the GC men a chance to strut their stuff. In short, it would be a real "race of truth".