I don't think there is any good to spin out of this. Obviously the idea here is to make the coasters more safe, but I just don't see this really doing that much. There will still be people who slip through with loose objects that aren't metal that have just as much potential to become a harmful projectile.
To be honest, I would rather see them get rid of the coasters than implementing these metal detectors. Hulk and Dragon Challenge are excellent, and it would be especially sad to see the the Dragon Challenge queue go, but they are still just coasters that you can get an equivalent experience with on other coasters at any number of parks around the world. People still get the misconception big-time that these are coaster parks , so perhaps by getting rid of them and replacing them with attractions on the caliber of Spider-Man, Forbidden Journey, Escape from Gringott's, etc., that could help to hone Universal's image in the public eye as parks where you'll have completely immersive unique experiences in the worlds of popular movies.