I find it highly dubious that any more than a small handfull of people are going to be able to pay for their subscriptions with their in-game created content. It seems like a marketing thing of "yeah sure, you can play for free, honest!"
First of all, most people who play games like this do so for the editors. Loads of people seem to get into games like CoH entirely because of the editors, and being able to customise their guys. Paying someone else to do it is like paying someone else to shoot the bad guys for you. Wheres the fun? I don't think theres enough game there behind the editor to justify paying someone else to make you a custom leather jacket. Especially since you don't use subscription time when your using the editors, which would be the only reason I could imagine for something like this taking off.
Second of all, RPS compares it to second life for the in-game items for subscription economy. The key difference being that creating things in second life is more than just cosmetic, its modelling and coding behaviors (as far as I understand it anyway). If you could make a gun in APB that shot further, or a car that handled better, then I can see a market. But for pretty graphics?
Anyone who's in a guild (or APB equivalent) is going to have free access to user-made content. Anyone is going to be able to make their own stuff too, sure it may not be as high quality as other stuff, but at least it's yours, which is kinda the whole point.
The only way this subscription thing is going to be worthwhile for anyone, is if the devs continually support the game with monthly updates after release, Asherons Call style.