User blog comment:Godzillavkk/If the Voice in the Darkness is the main villain of Starcraft 3, what should be the difference between him and Amon?/@comment-31277203-20180724203618

That's just Blizzard speaking with a forked tongue with the whole SC2 isn't the last game. You never really know what they have planned. Remember, as of Blizzcon 2017, Co-op was receiving the lion's share of development. In terms of story, we didn't even get the conclusion to Shadow Wars (remember part 6 still ended with a to be continued statement).

Personally I'm not convinced we'll be seeing SC3 until at least 2035 or later.