I'm also intrigued about gokyo as it's not one we cover very often, and I'd like to know if any/all of these conclusions I've just come to are incorrect or need reclarifying...
#1. Gokyo seems to rest entirely upon gripping ukes wrist with nages thumb nearest the hand, without this, we're pretty much doing ikkyo.
#2. Because of #1, gokyo is only available where uke's attack is non-gripping (i.e. can only be applied on strikes, with and without a tanto, and perhaps the 'dori' attacks that have yet to get a grip on nage (which are pretty much a tsuki at that point anyway) - which in turn reinforces the tanto aspect of the technique.
#3. If uke does get a grip, nage would now grasp the back of uke's hand rather than grasp below the wrist, (not that you would at this point!) i.e. gokyo is pretty much redundant if uke gets a grip - which again, ties in with the tanto aspect.
#4. Techniques such shomenuchi gokyo omote are not possible, as nage needs to reach ukes wrist from the offset, (and, assuming nage is entering as uke raises their arm for the shomenuchi, the wrist we are going for is out of reach for those of us without an orangutanesque reach)