I read up on the other stealth thread after jackards retort to my comment in the locks thread, figured I'd start a new one to continue the discussion.
Adventure -> Sneak : player starts sneaking, maybe a move speed decrease, maybe not
When sneaking, player data is not sent to other clients, thus not rendered, even with x-ray cheety hax client.
During day time, you cannot sneak when you're further than X from an object that casts a shadow (finite list of large objects).
During dawn and dusk, the distance around these objects is increased.
During night, you can sneak anywhere.
If you walk into the radius of a light source (or it moves into you) you are no longer sneaking.
Hearth fires and cave/mine entrance lights don't count.
If a player bumps into you (bounding box collision, detected by server) you are no longer sneaking.
Perhaps have a detection radius around people, perhaps not.
If you start aiming at someone, or initiate aggro, you are no longer sneaking (standing still and drawing a bow / swinging a sling is not sneaky)
Adding stats to the probability of any of those mechanics is unlikely to make said mechanic any more fun.
I've deliberately avoided talking about terrain types, as none of them (except maybe jungle/thicket) are clearly more "sneaky" graphically, maybe I'm wrong, but I don't think I'd pick up on that just as a player
You cannot start sneaking with other players within a given range.
If you are aggroed there is a cooldown before you can sneak again