I'm not so sure about this. Minecraft is a simple game that anyone can easily pick and play whereas KSP is more of a simulator that involves a much higher degree of difficulty, for example learning all the parts, how they would fit together to create a successful rocket, and basic orbital maneuvers. It's not that I don't think KSP will be popular, I think it'll definitely be a pretty big game eventually but not on the same level as Minecraft, due to its gameplay catering to gamers of all ages.