Watching the SAS assault on the terrorist desert camp in "Patriot Games" has always made me want sleeping A.I. for stealth missions.
A sleep waypoint could make an enemy unit sleep for an amount of time specified in the timeout settings. Loud noises MIGHT wake them up (at the Joint Readiness Training Center I would sometimes sleep through mortar attacks if they didn't sound near enough). If a cot or vehicle bed is nearby, it will act like a "Get in Nearest"; otherwise, the soldier will sleep sitting up (very possible after a day of digging a foxhole and filling sandbags) or across the ground.
A base alarm or shouts from friendly troops (especially commanding officers) will have a greater chance of rousing a soldier from sleep.
Of course, enemy troops can be stealthily killed while they are sleeping, either with a suppressed weapon or by action menu.