I've got it. I know what to do with Wit's End

+ = Madred's Bloodrazor

Grants IAS, MR, and- UNIQUE Passive Witless: Your basic attacks steal Magic Resist OnHit equal to 5% of your Magic Resist, stacking up to five times. UNIQUE Passive: Your basic attacks deal magic damage equal to 4% of the target's maximum HP.

The MR stealing would become a named passive the two items share to prevent them from stacking with each other.

So, why?

The old Bloodrazor was weird. It gave armor, attack damage, attack speed, and 4% max HP damage. It was generally consider a newb trap item since it just didn't work with anything particularly well. But the item detailed above? It synergizes well with itself, as well as with other sources of OnHit Magic damage due to the MR steal. Wit's End has issues because it lacks any form of scaling. It lacks anything beyond mid-game presence. Bloodrazor would afford Wit's a (very) expensive upgrade path to a whole new plateau of power. It would be a solid alternative for tanky folks to BotRK, granting stronger defense and OnHit, but losing sustain and a nice ranged slow.

But yeah, really expensive.

I could see an item like this falling in the 3.5-4k gold range pretty easily.