An NUC or similar SFF desktop PC seem to be pretty close to your requirements. Without an optical drive and without any spinning rust media, they're pretty durable. I use a lot of fanless PCs from OnLogic, Cincoze, and Neousys in industrial control panels...they have 'rugged' models that are designed to mount inside heavy equipment or prototype vehicles that you could probably use as a hammer, but even a consumer NUC will be fine in a backpack.
The form factor is typically more boxy, like 5x5x2" rather than 9x12x1", so they'll fit easily into a backpack but not so well in a briefcase. You can get them with laptop processors and passive cooling or the worst of both worlds - a whiny little centrifugal laptop fan, or you can get a luxuriously quiet 140mm desktop fan, desktop-grade processor and graphics that will blow any ultrabook out of the water.
However, they're not typically oriented for single-cable-connectivity. Why is it such a big deal to plug in one cable for the power supply and either a couple for the mouse, keyboard, and monitor, or one for the Thunderbolt hub?
The form factor is typically more boxy, like 5x5x2" rather than 9x12x1", so they'll fit easily into a backpack but not so well in a briefcase. You can get them with laptop processors and passive cooling or the worst of both worlds - a whiny little centrifugal laptop fan, or you can get a luxuriously quiet 140mm desktop fan, desktop-grade processor and graphics that will blow any ultrabook out of the water.
However, they're not typically oriented for single-cable-connectivity. Why is it such a big deal to plug in one cable for the power supply and either a couple for the mouse, keyboard, and monitor, or one for the Thunderbolt hub?