Cryptic is just ideal for him. There are several reasons, why:
1. No oaths ( except the first, which he's fulfilling constantly). He can do whatever he need. He is unbound.
2. He can speak four Trues for minute and become the most powerful Radiant in the Cosmere.
3. Perfect Surges for him.
But it maybe happened, I think. With Spook, in a final episode of A Secret History. It seems like Kelsier is just advisor, voice in Spook's head, but anything is possible.
Someone made a Nightblood-like sword with hemalurgically charged-metal, for example, charged by coinshoter powers. What will happen?
It will request a giant amount of energy, I know, because spike is already have Investiture in it.
In White Sand, we've seen a strange thing - terken. It obviously not Aluminum, but it makes the same- countering Investiture.
So what is that? Maybe, terken somehow depends on Autonomy? Or it works only against Sand Mastery?
Sorry for non-perfect English.