If we can make 2 billion people 10x richer than they are today, market/economic growth is not necessarily capped at 10x. Systems don't have to be linear.

As a contrived example, I would imagine that folks living on $2/day probably buy on average effectively 0 iPhones/year. If somehow they had 10x the wealth they do now, they wouldn't buy 10x the number of iPhones they could previously buy... they would buy almost-infinity-x the number of iPhones they previously could buy, thanks to division by almost-zero.

BTW, my point is not that this is some kind of arithmetic trick, but that 1000x growth just depends on how low the starting baseline is (which is very low, by almost all measures of baseline economic activity/wealth of the $2/day demographic).