PWI is ahead of private servers in terms of expansions, since patchs on private servers are implemented as the files of expansions turns public.
Good fashion we have plenny of those, with the + of having even custom ones made by GM Echo. This without the fact of custom weapons\name color\titles.
Set Card bonus is something that can get broken really quickly, it would be one more thing to worry about balancing, it would also lock people into a Meta, while with no set bonus people have more freedom of build (crit\full suport\full s+).
Have in mind that in PWI theres people from level 30 to full r9 ones, balance takes in consideration the entire picture of it, while in private servers everything is based on the late game of what PWI would look like.