Let's get one thing straight, no one is going to be purchasing their way from r1 to r40, won't and can't happen. What will most likely happen is smart players will pick up a free War Tract that you can get in game along with a paid one to skip the last two mind numbing levels up to r40. Sorry but the sky is not falling, this is not going to unbalance the game and WAR is not going to die from this.
WAR is a pvp game and a players Renown Rank is actually more important in the end. With the accelerated renown gain from the Progression Pack players will still need to gain the emblems/crests to purchase the high level gear.
In the end no one really knows what effect patch 1.4 will have on WAR till it's released. But I am going to go out on a limb and say that things will turn out just fine.