I would settle for starting with a slow walk/silent mode. Based on your characters dexterity and intelligence (you need to be smart enough to figure out where not to step (on leaves/sticks etc), and not super clumsy, in walking slow and silent. Hence making less noise (half as much).
You could have it always work, but based on the numeric formula/average whatever is decided of dex and int, is how slow you move. So yes you can do it with 8 in both, but you would move like 5x as slow. While higher stats would reduce this. Make it take something like 30x30 to move at what is normal movement.
Later on you can add skills for it, that would just build into this movement mode.
So this way you can have the mode, but until there is a proper skill it take more time, a lot more time. If a zed spots you, and you don’t stop trying to move this way, it’s going to catch up fast. Hence drawback.
It would also help avoid some of the ‘horde’ mode… and why 90+% of all players just turn it off.
