A question about Luden's Echo / Expected synergy with Veigar

For those of you who don't know, there is a brand new 120 AP item on the PBE right now called Luden's Echo. It provides 120 AP and +7% MS. On top of that, it has a unique passive that build charges as you run / cast spells and then deals 100 (+15% AP) Magic Damage to up to 4 targets (including the one you hit) with your next spell. I think of it as the AP Static Shiv.

My question about this item is what happens if the charges are expended on an AoE or multi-target spell? For example, if Karthus ults with full charge will all 5 enemies proc the passive?

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The other thing I wanted to ask was if this item had anything to do with the recent Veigar nerfs/buffs. This item almost feels like it was made for him, and it was first teased around the same time the Veigar "changes" were unveiled. Veigar is an immobile infinitely AP scaling mage, and so an item that provides a crap ton of AP, some MS, and a passive that can deal some notable damage with high AP feels like the perfect DFG replacement for him. Not to mention it gives him some very light multi-target capabilities. [On another note this items (+15% AP) scaling pretty much makes up for the 20% AP ratio nerf to Veigar's ultimate, however it makes it much more situational damage rather than consistently hitting for huge numbers.]

I do have a feeling that the two were tied together and I really love Luden's Echo so far. However, if this is the case, I really wish Riot had released Veigar's changes and this item at the same time. It would've cushioned the blow significantly. Regardless, I think that Riot is on the right track now so kudos to them.