Another idea for a "cloak allies" mechanic: A Ward that stealths nearby allies, but not itself

I've brought up the idea of a Champion who can stealth an ally before, though there's always the problem of it ruining certain Champions' counterplay (i.e. Malphite, Amumu, etc). Still, I feel such a mechanic CAN work if it has various drawbacks.

One good drawback would be that it has to be localized to an area, not a direct-target buff you can apply to an ally. This way, your opponents can stay away from the "stealth zone" if they don't want to receive an unexpected Malphite ult, or they could throw a Sweeping Lens effect down on said area to render it (mostly) useless.

But another thought came to me while playing some Starcraft 2 Co-op missions as Vorazun: What if that stealth zone were dependent on a visible ward placed by a Champion?

See, one of Vorazun's mechanics is that she can place down a Dark Pylon that does everything a normal Protoss Pylon does, but it also cloaks nearby units and structures. Obviously it doesn't cloak itself, so it can still be attacked without detection.

Now imagine a skill like this (rough draft, take with salt):

Ghostly Crystal Place down a special ward at target location that grants stealth to nearby allies in a modest radius. This ward has 3 HP and is visible to the enemy at all times, even if in brush. Lasts X seconds (i.e. 10 seconds max).

This creates several drawbacks to the "stealth on ally" mechanic: First is that the ward is always visible to the enemy; even if you place this ward in brush and your enemies don't have vision within that brush, it can still be seen and killed. Second is that if the ward is killed, the stealth zone ends. Third is that it trinkets counter it because it's area-localized; use Sweeping Lens on the stealth zone and you'll be able to see the enemy in it (even if you can't directly target them). Last is that said area is short-lived; 10 seconds would be pushing it, and I think a 4/6/8 second duration would be more than adequate given the amount of potential.

I'd like to know, however, if this change would make the mechanic acceptable. If it can be countered in so many ways, it may not be quite as strong as it seems all the time.