Would Blizzard encrypt the files if it's just for an updated starting zone and that's it? Doubt it.
Would Blizzard encrypt the files if the next expansion is themed around death / shadowlands with the Lich King as an important figure? Yes they would.
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What if... Sylvanas and Bolvar meant for this to happen from the start? Lich King and Queen.
They even got Azshara to help them overpower the Horde, Alliance and the Old God. What's stopping death now? Nothing. Seems like that is exactly what Sylvanas hints at with her words in the cinematic.