Aliens may not be invading or fighting the human race, but their presence is certainly a part of the reality change!
Whatever this cascade may be, it seemed to fancy humanity's interpretation of extraterrestrials... from the 60's!
Humanity would slowly be defined by the B movies of early America:
Still human-like with soft squishy grey skin, deep beady black eyes with a bit more wideness to them, fingers ending in tender nodes, and bouncy antennae peaking on the top of their heads.
Diversity would no longer be an issue, though it seems intelligence may be as 'simplicity' becomes an obsolete idea.
And to top it all off, they would be ruled by their alien overlords, though by the time the cascade finishes, the idea of 'alien' would replace the definition of 'humanity'