I assume they could effortlessly ramp to $1B if that estimate is semi-close. It would cost virtually nothing to add more paid markets and services; maybe allow the gravity algo to be tweaked.

Figure very low costs for a site like that you could make your money back in 5-6 years; which is insane at that scale. I bet if they put it up for sale for $3B it would be sold by the end of the week