Interesting to see Ars Technica talk about Blizzard's Instant 90 coming in WoD

I don’t usually see Ars Technica talking about World of Warcraft. Maybe I’m not looking for it, either. As a person who has 2 level 90s and a handful of toons in the 70s, I find the option to purchase 90s appealing. What I really want Blizzard to do is allow for users to purchase a prorated option for leveling toons to 90. What if I want my level 71 Monk to be 90? Can’t I pay a fraction of that cost?