So this suggestion is apart of a multi-suggestion series, so prepare yer minds! So rifts are no longer just one chunk. Rifts start out in chunk based lines like a crack, but can grow and over time will become ellipsoid shaped (almost like the 10th doctor doctor who logo). Rifts have a spawn rate multiplier for mobs, the multiplier size depends on how big the rift grows. Rifts have a chance to naturally grow, but they mainly grow from uses of the rift manipulator (read the rift manipulator post for info on it). Rifts are detected by some sort of handheld device (not sure what name yet) like the scanner devices used in torchwood. They tell you thinks like rift size, multiplier, activity, etc. When mobs fall through the rift there's some sort of animation glow like in the torchwood series. Rifts are also rarer now, to make sure the world isn't flooded with mobs and also to make it more accurate.