I'm going to make a guess/prediction that the CLS system will remain at three groups for a very practical reason - the time that it takes to complete the CLS signaling and preflash sequence. The more groups available, the longer the sequence will take, and there is a practical limit to how much time can be spent in this sequence prior to exposure in real life photography.
In fact, some of the links previously referenced look at this issue in relation to eye blinking at the time of exposure. At the time, the D70 and D2X were current models, and it was found that the preflash sequence using the built-in flash on the D70 operated slowly enought for the exposure to capture the blink caused by the light from the preflashes, while the D2X (SB800 as commander) was rapid enough that the exposure occurred before the eye could blink.
The analysis was one of the factors that has led me to believe that the preflash signalling protocol is not highly depending on a timing pulse because of the apparent differing speeds with which these two camera models could accomplish the preflash sequence, making me believe that there is something in the on-off pattern of the preflash that controls the response from the remotes.