About twist that can be done on Luden's Echo

I thought the New 120 AP Item is a bit weak. First, if you are targeting a single target, the additional 100 damage given the low proc rate doesn't mean a lot, Rabadon's Deathcap provides much more damage. If you are aiming for wave clear, it is even worth since the damage is low and it is hard to proc many times. Talking about Statikk Shiv, I personally think it is a much better item. Casting spells ususally consumes mana while auto attacks don't, and Statikk Shiv gives the opportunity to crit, also it is mix dmg (which diverse the dmg type) Comparing with Lich Bane, Lich Bane has a higher proc rate (1.5 sec cooldown and much more consistent since auto attacking doesn't need your spell to be off cool down). Dmg from lich bane also is much higher too (15% vs 75%).

So, I've discussed this with my friend, and he proposed a better (imo) replacement solution for the Deathfire Grasp. It could use the same or similar mechanics to build up the stack, and upon full stack, it buffs your next spell's dmg by 30%.

A few twists you can do to this proposed item. If needs buff, you can make the stacks consumes on hit instead of on cast (doesn't waste the stacks). If needs nerf, say aoe abilities with 30% more dmg is too OP, you can make AOE abilities only have less (say 15%) DMG increment. Also, you can use other types of ability amplifiers too, say next spell has 30% additional magic penetration or so on.

So what do you guys think? and @Riot