I think having something similar to sudden impact on mages would be useful, magic penetration is such a useful early stat and I think a rune that incorporates that would be a really good addition. My idea is to gain magic pen after using an ability that costs mana, on a relatively long cooldown as to not make it entirely broken. My only issue is it being incredibly broken on people like leblanc, as its meant to be more of a mage thing.
Maybe something like Cheap Shot - your abilities deal X% increased damage against champions with impaired movement or actions OR impairing the movement and/or actions of an enemy champion increases your damage against them OR either of these reduces their Magic Resistance by a flat amount.
I'm not going to be like 90% of the toxic community on these forums and tell you that your idea is bad regardless to whatever it is. I fully agree with you on this, there, should be a mpen rune that suits mages.
Ideally, 20%flat magic penetration and 30% mana cost refund on mana spent. Essentially a nerfed void staff that refunds some mana spent. So if you have 500 ap you would get around 200 mpen damage, If you had 100ap you would get around 35 mpen damage. hmm that sounds too op in fact, lets go with 15% flat mpen, seems more realistic > 100 ap is 15 mpen, 500 ap is 75 mpen
