Doesn't make sense to me. Snoke is dead.
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Dude got cut in half with a light saber. Snoke was not projecting himself. We saw how that works with Luke. Luke could not be sliced with a saber. He could not be be killed by a firing squad...not even touched. Snoke got cut in half. It showed him very dead too. When Johnson said we learned all about Snoke we needed to in last jedi, I believe he meant it. We. saw Snoke for what he was. An evil puppeteer using Kylo and the first order to carry out his plans of universal domination. Snoke's character is simple, and uts confusing, and its angering because you want his character to have more of an impact, to be more like Sidious. But, Snoke is a simple character no rounding out neccessary. It sucks, its to easy. Snoke who claimed he could read Kylo's every thought should have seen it coming. He made himself look so powerful throwing Rey around and punishing weakass Hux.
Bit, in order for Kylo's character to become truly powerful he had to take out Snoke, the only and last thing standing in his way to the top...to the dark. Snoke served his purpose. We won't see Snoke again.
As for Luke, we will see him as a force ghost in IX.