But I'm not really thinking of kata themes in that manner anyway. The problem, however, when you think of different katas exploring different themes, it seems to me, is that it raises so many other questions, regardless of whether or not you get the themes right. For example, if you suggest that Seiunchin is a kata that was created to explore responses to pushes and grabs--since that is certainly not enough to base one's self-defense on--then other katas would be needed to explore other self-defense scenarios. That in itself presupposes that some or all of the katas go together in one system, whether they were created that way or whether they were merely collected and put together in that way. Which raises the question: Is it a complete system? Of course, this thematic analysis of kata is based on bunkai or application of moves, which itself is a matter of some disagreement or at the very least multiple interpretations.
In any case, I find it an interesting exercise because it is a way to "see the system" or at least a way to organize a seemingly random and large collection of techniques. For example, Kururunfa seems to be a thematic exploration of one kind of an outside block--the defender's right hand blocks the attacker's right punch or the defender's left hand blocks the attacker's left punch. We see this over and over again in the kata. In fact, all of the initial or receiving "blocks" seem to show this, in various forms. There is some variation; that is, sometimes it is shown with the hand vertical, sometimes with the palm up, and sometimes with a palm-up hooking block. Seipai, on the other hand, seems to be a thematic exploration of another kind of an outside block--the defender's left hand blocks the attacker's right punch or the defender's right hand blocks the attacker's left punch.
The problem is that Seipai is also about "twisting the head off." This comes up a lot in the combinations of the kata. And Seisan seems to be a thematic exploration of the "sun and moon block." But one of the problems here is that the Higa dojo (Shodokan) seems to be the only school of Okinawan Goju-ryu that even does the sun and moon block in Seisan kata. And how are we to look at Shisochin? Is it an exploration of four direction fighting, as its name implies--responses to attacks from the front, sides, and back--or is it an exploration of how to use the forearms in blocks and attacks? Is Saifa a basic beginning kata that deals with responses to grabs, pushes, and punches--why it's taught first? Or is it taught first because it shows how to use the waist or koshi?
In any case, I don't think this is a fruitless journey or pointless question just because there is no definitive answer. The understanding you gain is certainly beneficial to your ability to see variations within the different kata and beneficial to your ability to use each of these techniques.