Atma's Impaler Rework

Yes, once more, one of these. You probably already are pretty fed up with ideas how this item could be brought back into the game without breaking it (again).

With that out of the way, let's begin describing the idea. First aspect of it, Atma's now gets a building block item. Like this one:

Rusty Halberd
Build:
(720) + (360) + 270 gold Stats:
40 Armor (720)
10 AD (360)
Unique Passive: Vitalized - You gain bonus AD equal to 0.75% of your max. Health (Max. 15 AD) (540)

But why would you cap the passive bonus AD?
Simple, because you can calculate best- and worst-case scenarios for the item now, and assign the passive a real gold value. Also, makes the item worse for champions who do not build extra health (aka traditional build carries). It also limits the abuse defense -> offense conversation that resulted in the dominance of the Atmog's build back in S2.
In addition, it gives a building block item for further items.

With the abuse case out of the way, one could make the Impaler an interesting item:

Atma's Impaler (3150-3300 gold)
Build:
Rusty Halberd (1350) + (300) + (730) or (800) (Prefer the Cloak)
Stats:
65 Armor (1300)
10 AD (360)
20% Crit Chance (1000)
Unique Passive: Vitalized - Gain 1% of your HP as AD. Max 30. (900) Unique Active: Impale - For 4 seconds, gain 20 bonus Armor Penetration. 60 seconds cooldown.

This would be a slot efficient, late-game effective variant of Atma's Impaler, designed for champions who can weave in a good amount of autoattacks as a form of sustained DPS. Is it an item for everybody? No, certainly not. But that's not the pretense for this item.
First I thought of giving the active high ArPen for a single AA, but then realized that would shift the focus away from sustained to a rather bursty form of damage, defying the purpose of the item.
All number are, of course, pure theorycraft and rather abitrary. Like the concept, but not the numbers? Leave a comment, pls, and explain why.