Elusive gives me an idea on a new perk idea.
To preface this: I LOVE the fog vials, but I feel even using them as intended they don't provide much utility. They are too small in range and take too long to expand. However, Perhaps they could be improved by perks? I know it's an annoying habit of slapping bandaid solutions onto things through perks, but it's better than leaving a mediocre item as-is.
Simply put: If you are standing in the area affected by a fog vial, you would gain 7-10 seconds of elusive when you leave the area. This would make the small range of the fog vials less of an issue AND would make stealthing more viable. However, to counteract this, any generator in the area takes more regression damage on break while the fog is present. You are essentially sacrificing some gen progress for a guaranteed avoidance of the killer.
In general I think fog vials would make perfect "supportive" items for perks to alter and improve. Heck, because it would require an item that ALREADY has a cooldown, that's an inherent downside that makes them easier to balance!