Wouldn't the "Overheal rune" be better ..
As a support rune?
For example a X% of all your healing abilities on allies that exceed their max HP is turned into a shield that decays over Y seconds.
Making it short would mean that the support would need to time it right.Using it too early would mean that most of the shield would decay before the damage is dealt,while using it too late would just waste the effect.
I would be an interesting for skill expression and timing. It would be honestly really good on Soraka,as it could her allow her to play pro-actively instead of just passively.Tho with the new rune system (especially Aery) she's doing fairly well with maxing Q.
Good or bad idea?