What a great thread you've started here. And great responses too.
I do not want to be redundant here. So I'm going to make a few points. Isolated, they may seem disjunct. But taken in the context of the other good responses, they will add to what has already been said.
Since I know you, I'm not quite sure exactly why you are so concerned with chambering. But let's address this, and I'll separate it into lead attacks, follow-up attacks, and counter attacks
First of all, I don't even allow a white belt to chamber on the first (lead) punch. And I know for a fact that George does this the same way. The very first attack should be done in a manner that considers that you are attempting to bridge the gap between you and the opponent, and do it without getting nailed in the process. Pulling the arm back to a chambered position or doing anything that would "telegraph" your intent would indeed be suicide in practical application. At the very least, even a beginner should throw the very first punch from sanchin, realizing that one is basically attempting to do the real damage once you have entered into the fighting range.
OK, so now what about the subsequent attacks? Well from the attacker's standpoint, a great lead attack that explodes into the defender and puts them off balance affords you the time and protection (best defense is a good offense) to chamber the subsequent technique - IF YOU CHOOSE TO DO SO. A chambered attack will have more power, so should be done if you ever set yourself up to do so.
What about on the defender's end? Well basically in blocking, one really never chanbers in kyu kumite until the end. And the way I teach kyu kumite, I tell people that THIS kumite is all about completely controlling your opponent before delivering your counter-attack. Again - as I teach it - you should have AT LEAST a half second where you have grabbed and controlled the person you will hit. If you aren't, why not? Might as well close the fists and do generic blocks and play the one who hits the most/first wins. So....IF you have controlled your opponent, you now have the opportunity to bring your fist way back in a chambered position and send it through your opponent until you envision it coming out the back of their gi. THAT is what control affords you. No control? Better not chamber!!!
Yes, Tim, the advanced student who has developed the Bruce Lee patent-pending one-inch punch can resort to just doing a quick, explosive, whole-body attack from the sanchin elbow-up-front position. But 99% of practicing karateka aren't there....yet. So in the mean time, you do what it takes to make this counter attack count. This means that a beginner needs to chamber more than an advanced student TO ACHIEVE THE SAME OFFENSIVE END.
What about in real life? Well watch a really good boxer in slow motion some time. When the left hand goes forward, the right hand comes back....some. Even in the best. No, it doesn't come all the way back to fist-beside-rib position. But there is a certain degree of "mirroring" that one does between limbs that affords the best power for individual movement and the best flow from movement to movement. This means that chambering happens in real fighters and real fights, but not to the extent that you see it when a kyu rank is just trying to feel and experience the motions and the kinsesthetic sense of the flow (thoughts that Shelly expressed herself).
Stepping back twice is a problem? Where were you when Gary Khoury was teaching his sparring classes last camp? (And I know you were there.) Gary and I "spar" a lot in our ideas, but this is just the fighting spirit that two passionate karateka display. Actually when I view someone like Gary teaching sparring moves (as I did in August), I see him do things that even he doesn't know he does well. I even told him that after viewing his class. One of the things that Gary was teaching was how to handle a charging opponent, and counter when the time comes. You know what? His foot movement was RIGHT OUT OF KYU KUMITE. And the blocks were all there. No, Tim, he was not doing two full circle blocks. But he was demonstrating how he would step back several times until he got back in his left stance and had his right hand (he openly admits he hates to hit with his left) cocked and body coiled, ready to explode. Then BOOM, he fires a body-stopping blow that wins him a point, and in the real world might set him up to finish off an aggressor.
This is not unlike how a real fight may progress. I personally am not one to throw the first blow. That's my personality and disposition, and I need to deal with it. In several instances I've had someone attack me and it took just a brief period of time to realize what was going on and how I should respond. In the 2 circumstances I am thinking of, they got several attacks off, and then my own right (I'm just like Gary in that sense) exploded without me even realizing what had happened. And yes, there was a brief "retreat" period before I had my wits and my balance about me. Yes, that is a real attack/defense scenario (in my own very limited experience). The good guys don't usually hit first, but they do hit last.
When we get good at this though, we no longer do linear movement back. Mike Murphy alluded to that in his response. Diagonal stepping is a start. The REALLY good ones end up with net forward movement (even if forward and slightly to the side). It's hard to do that in kyu kumite without interrupting the flow of the exercise. But in reality, we should be so lucky or that good that we make a perfect response to the fist attack....game over.
As they say, timing is everything. And in this case, I am speaking about the timing of one movement in your body with respect to another.
Let's take it at the most fundamental level. When most beginners attack in kyu kumite, they 1) step, 2) punch, 3) step, and 4) punch. When they get a little better, they don't wait until they have completed the step before they begin the punch. That is suicide. You do not walk into someone's attacking range without something to do (preferably an attack). So at an intermediate level, the person completes the attack at the end of each of the steps. But the process should not stop there. Good fighters do not waste energy. When your foot makes noise at the end of a step, you are dissipating energy. What a good fighter will do is lead with the attack, and make the fist hitting the target be a sound that happens before the feet stop your body. I call this "break timing". That way, you send more energy into the opponent, and THE PUNCH GETS TO THE DEFENDER FASTER. In fact...so fast that it's very difficult for the defender to recover. This is kyu kumite at a very advanced level.
The same can be said about the timing between the block and the counter. In the beginning, it's block/chamber, then counter. But in the end, you can - on some techniques - change the timing so that the block and counter occur simultaneously.
Yes, Tim, if I were the Uechi King and my subjects had to obey me, I would choreograph a new kumite. But I think I would leave kyu kumite alone. As Paul_C says, it is "kyu" kumite after all.
For my renshi, I submitted a series of partner exercises that were interpretations of the hojoundo. I went out of my way to do things different. In many cases, I used sliding steps instead of full steps for the attacks and defenses. But you know what? I find that these are very difficult for people to learn. Hmmmm.... part of my development of those 12 exercises then was to separate them into beginner, intermediate, and advanced ones. And the difficulty with the intermediate and advanced ones had more to do with movement than anything else.
Wierd....even though movement is so crucial to good fighting, it is one of the last things that a student of fighting absorbs. All the beginners really know how to do is stand still and swing. It takes a while before they can walk and chew gum...play the guitar and sing. We need to take it one step at a time (sorry...).