I thin poor ppl won't use it, but you don't have to be rich.Who will use this service?: Rich people who want to multibox.
Leveling from 1-90 costs around 70-80 hours (incl. professions).
So if you are a working casual you have 10-20 hours playtime a week, maybe you are raiding 10 hours a week, so you have 5-10 hours a week left for a new alt.
Most ppl i know find leveling boring as hell. So you spend 2 months on something that is boring.
Or you buy a character from blizzard for the price of 3-5 hours of work.