Honest question and observation here without any snark: Are other user groups requesting buff trails? I hike in wiss almost as much as I bike there, and while hiking I generally try to avoid the smooth fast trails now and stick to the technical hiking only trails. Way more interesting and less likelihood of getting creamed by a bike.
I'm not entirely convinced that the smooth trails will turn rocky and technical over time. The trail above kitchens lane is now quite a few years old and it seems smoother and faster now then it was when it was built.
It is not really a question of people wanting buff trails. There are many areas in the Wissahickon where the soil doesn't contain significant quantities of rock. When you build in these areas you end up with a smooth trail. Examples are Houston Meadow, the trails running down from Bluebell Field, and Kitchens Lane.
You can go into the woods and collect rock, but this is land that has been farmed and rocks have been removed to allow plowing and to build structures. Often there is no rock to be found nearby. What rock is found is used to build retaining walls to protect tree roots. There just isn't enough rock available to make rocky trails.
Roots are another feature that makes a trail more challenging but the park won't approve a trail that goes across exposed tree roots. The Wissahickon has an old and sick forest and the park wants to protect what is left. Over time though, roots are exposed and the new buff trail becomes rootier.
Will the trails become rockier? Some will but it may take decades for rocks to rise up through the soil and for soil to wear away to expose the underlying rock. Trails like the Golf Course Climb already are getting rockier since the soils there contain a lot of rock.
What can be done to make the trails more interesting?
1. Show up for work days. Collecting rock in the woods is a lot of work.
2. Make your voice heard. Call the FOW office, show up at FOW's yearly public meeting, build alliances with other sympathetic groups like the trail runners.
3. Don't sanitize the trails. I know its tempting to shortcut when you are tired, don't do it. Stop riding around steps and widening the trails. If there is a rocky switchback don't cut down all the bushes next to the rocks in order to avoid them. If there is a log that you can't clear don't cut it out, notch it or ride around it. Get off and walk.
The mountain biking community has become much more influential in the past 10 years. There are mountain bikers on the FOW board, trails all over the city are being designed and built by mountain bikers, and features like log rides have become accepted. You can help by getting involved in work days, advocacy, and by educating yourself and others.