the next 1000x in 4-5 years

At the risk of stating the obvious, Ars is working backwards from this metric to get their headline "double every 6 months." 2^10 = 1024, to get that number in 5 years means doubling every half-year.

But Google didn't set incremental 6-month deadlines for 5 years straight, they set a single 5-year deadline. Because in 6 months shareholders can call their bluff quite easily, but in 5 years they're hoping everyone is A) distracted by some new disaster, or B) there's a new tech hype cycle they can push. They're trying to stall the bubble popping by pointing to a nebulous future where they magically scale to infinity, and hoping we all forget that they ever made this claim.