I thought Holocrons stored recordings and other information. Snoke clearly isn’t a recording since he’s talking about real time events in TFA to both Kylo Ren and Hux.
If it works like Jor-El/Kal-El in Superman, then Snoke could be someone who’s dead. I just think it would be a bit convoluted. But not 100% impossible.
He could also be a Force Ghost, but in this case why using a hologram and not just appearing as a ghost? (to hide the fact he’s a ghost? Convoluted, also)
So, for now and until we have more proofs, I just think about Snoke as someone who is alive.
Probably Plagueis (to somehow wrap the whole saga. I’m all for it).
My biggest fear would be that Snoke is Rey’s father (he only looks weird because of his injuries. He looks to me like he could be a human). If it’s the case then Episode VIII will somehow plays along the lines of Empire, like TFA played with ANH. And I want Episode VIII to tell us something as new and fresh as possible. ANOTHER family reveal, no thanks.
EDIT: that’s said, it would maybe be more intersting than if she’s Luke’s daughter.