DARPA boasts that the system can snag a "full-size" drone, but don't expect it to catch any Predators. SideArm can snag a drone as heavy as 1,100 pounds, which means it's not quite strong enough to catch the plane-sized Predator or its larger siblings. There already exist rail-and-hook systems to catch small and medium-sized drones like the ScanEagle. In those systems, the drone deliberately flies into a tall net, halting its momentum. DARPA's experimented with alternative landing and launching systems before, like this quadcopter-launching body and sky hook, with modest success.
DARPA has been mostly focusing on making new things, pushing the boundary of what is possible to build. Case in point: This new challenge it issued to hackers. The challenge aims to solve a persistent problem in computer systems. Flaws in software often go unnoticed for around 312 days, time which can be exploited by hackers. And then once those flaws are noticed by a human, they still need to be understood, patched, and then released out to the broader community.