While it seems like this there's a sad fact that those channels are almost guaranteed not to be spam channels who create actual content. 100k is a good barrier for them to set for access to such a powerful feature. Content ID takes a lot of computing time and power. By giving a single channel access to it they have to add and index hundreds of thousands of videos to the database every second of every uploaded video is compared to. The tool was originally just designed for music until movie companies started to complain. It has a ton of false positives (See the support forum here or your email inbox to get a taste). If they give everyone access to it there will be even more false claims "solidified" by Content ID matches. Also without access to numbers I don't think many videos of channels under that number are even reuploaded. It never hurts though to look over your most popular videos and to search for similar videos to find potential reuploads and to take them down using the old DMCA form. Freedom! might be able to use it's CID access to do this for larger partners (by setting the thing to "track" for those assets, not sure if that's possible for only some things though) but I don't think it's what YouTube wants the thing to be used for... But who knows, maybe one day computing power will grow on trees and they can open up access to it but at the moment that's highly unlikely