My main concern with stealth is how game-breaking it will be even early on. In most games that have stealth mechanics it quickly becomes a “Joker” in any combat situation.
A base full of enemies? I sneak by and stab them in the back.
An entire horde homing on me? I sneak by and stab them in the back.
A miniboss? -||-
ANYTHING? -||-
Sneaking should be a “support” skill simply letting you accomplish a small task without attracting attention. A character with 0 stealth should still be able to remain unseen while not moving or moving slowly behind an obstacle, while higher levels should only decrease the likehood of being spotted if our foe gets closer or behind partial cover.
Dishonored, I’m looking at you. Strolling into a palace on the highest difficulty and walking next to everyone… But you’re in partial shadow, they can’t see you. Don’t even get me started about stealing (stealing, not snatching/kidnapping) guards. From full rooms.
On a related note, high grass plz. And perhaps occasional 2-3 cars blocking the road sideways, to give us a chance to get to the other side when you can’t wait for nightfall.
BTW, check out Dwarf Fortress’ stealth mechanics. I especialy like how there is no button “begin sneaking” - the game assumes you’re not actively trying to catch attention as long as you don’t run up to someone and smack him in the face. You slow down and sometimes go prone instead of “press to vanish in the night”