I believe the Zipline was added by another Co. that charges a fee and the park gets a percentage.
The Non-Profit that runs Eagle Creek, "Friends of Eagle Creek" Didnt even want mountain bike trails in there.
I really dont think a DG course will ever be installed.
As I wrote in my review of N.W. way Park. "it needs to be pulled & moved to Eagle Creek"...... sadly I really think it wont happen.