Should you be rewarded for not using stopwatch?
As it stands taking stopwatch reduces the cost of zhonyas with stopwatch is 2600 (rune) and 2300 (bought). So if you take the rune then using stopwatch has no downside as far as upgrading to an item. Quite a few champions benifit from stopwatch and it is only slightly contested by magical footwear. Making it the rune you usually take in that tree.
While I'm not implying stopwatch needs a nerf I think using stopwatch should reduce the amount of gold you get off of your item, Or increase the amount of gold it cost to upgrade you could say. It just makes more sense to work that way no? It is a broken stopwatch after all. That way playing to conserve stop watch would have a upside and players would be rewarded for playing safely; Rather than rewarded for taking risks because of the free invulnerability.
I don't know how you would go about balancing it as far as the entire tree goes but I think it would make a lot more sense as a mechanic. Thoughts?