The main difference is Spellvamp had AP, Death's dance does not. AP Users like Vlad and Swain were in lockstep with WotA. They're unlikely to sink 3k gold into that passive.
The same question is running in my own head.
I don't see how you don't rush this after gunblade on Kata and Akali now... maybe you don't. But I feel along with Ravenous Hunter, there's definitely potential for abuse. We'll see how it goes.