Testosterone is a crucial hormone to maintaining the male reproductive track as it enables spermiogenesis to occur. Testosterone is only able to work in this fashion with the help of the androgen binding protein which concentrates testosterone to the testes (which is what eventually leads to the biochemical cascade that results in having your testes the size they are along with the maturation of sperm namely). Now when I see that the study showed that testes were reduced it makes me wonder where all that excess testosterone is going, or if it's even produced at all. This is where the psychological effects come into play, which is something we can't quite study in mice with any real confidence.
I'd wait until it gets to humans before taking this seriously, because the research field is constantly in the stage of animal testing (the lab I work at is a great example!)... the majority of which seldom make it to human trials and even further on, market distribution.
Also, I have no idea what the hell BRDT (the protein the JQ1 targets) is, flipping through my text and common knowledge, it must have another name... and it must be part of the aforementioned cascade above. Google didn't help me out either.