D&D Next: Surprise

I am somewhat astonished that the D&D Next playtest packet has no rule for Surprise. It simply says "The DM determines who is Surprised." How far D&D has wandered from its roots that such a core provision isn't deemed important enough to be playtested...

At any rate, here is my House Rule for Surprise in D&D Next, using the preferred d20 engine.

Surprise 
First the DM determines whether any side of the encounter is Hidden or in the open. A Hidden force has taken the time to lay an ambush, either because they know the other side is coming (aka, an ambush) or they are opportunistically waiting for the next mark to come along (like bandits).

If one side is Hidden, the approaching side makes a Perception contest opposed by the hiding side's Stealth roll. Depending on how much time or effort has been invested into Hiding (making blinds, wearing special camouflaged clothing, or deploying helpful magic), the Hiding party can have a significant bonus to their role. Success indicates that the approaching side notices the hidden side before being attacked. Failure means that everyone on the approaching side is Surprised.

If both parties are in the open (as with a random encounter, or if a band of adventurers stumbles into a monster's lair), both sides make a Perception check opposed by the other's Perception check. Each PC makes their own Perception check, but the DM may group monsters for this purpose. Winning the Perception contest by 5 or more means that you were paying more attention and thereby gain one round of Actions while the other side is Surprised. Any results with 5 or less points difference means that no one is Surprised and initiative is rolled normally.

Characters or Monsters that are in the open may be Alert, Relaxed, or Distracted. Most of the time, you are Relaxed, even when in a dungeon, as maintaining an Alert status requires a WIS check each turn (DC 10), and once lost cannot be regained for 1 hour. Alert characters or monsters have Advantage when making Perception checks, and Distracted characters or monsters have Disadvantage. Sleeping or unconscious entities are automatically Surprised.

Once Surprise is determined in a dungeon or urban environment, multiply the highest successful Perception roll by 5 to determine the initial distance between the parties in feet. In the Wilderness the multiplier is 30 feet. If there are no successful Perception checks, the Hidden party dictates the encounter distance.