There are some odd interpretation of the two channels; things like go/no-go and such.
Once you place the channels in a larger framework of motor control most of this falls away and it starts to look like the true purpose is something more mundane like extend & retract.
Please see this paper, particularly section 3, with attention to the bit about posture - a mouse balancing against external forces.
Henry H. Yin, How Basal Ganglia Outputs Generate Behavior
I hope this will give you some background to make an informed evaluation of this proposed model.