Could Nightblood theoretically be turned into a Hemalurgic spike?
The problem with that is that Nightblood is already invested, so it depends on your version of ' Hemalurgic spikes'. Piercing someone's body with Invested metal can have weird effects all through the Cosmere, but ripping off a piece of a person's soul using an un-Invested spike to Invest it and create one is different... we're talking about two different things, right. So there's the.... so what is a Hemalurgic spike? For instance if you've got a spike that's Invested and you stick it into a Kandra on Scadrial it will still work as an Invested Hemalurgic spike. Making a new Invested spike by ripping off a person's soul, that's a different process and a little more difficult to accomplish and requires some specialized knowledge.