I think some reaction channels are absolutely brilliant. It can be so much fun to see other people have an opinion on something that either matches yours or may be completely opposite. However; some react channels forget to 'react' in their videos, if you know what I mean. Just posting your webcam over someone elses video is, in my eyes, not creative, abuse of copyright law and most of all; not entertaining.
I think that it is very likely that at some point me and my partner do a react video. However, I do not see it very likely that we will make a video solely about reacting to another video/channel. It would probably be just a small segment of something bigger.
I agree about the blowing up tho; react videos, if done correctly, can be a very easy way to grow a channel.