This might just be a misunderstanding on my part, but my assumption was that Hasbro ships from China on a, more or less, constant basis. Therefore they wouldn't exactly be just "hoping" an acceptable variety ends up at the stores. My thought was for Hasbro to have a more steady stream of figures. Essentially they would have (taking this year as an example) started out with Luke, Han, Ben, Spacetrooper and the aliens shipping. Then once that's been going for a bit they sub out two of the aliens for the Frigate Luke, then after a week or two they sub out the Spacetrooper for the Hoth Trooper, then they replace Ben with Needa, and then Luke and Han with Leia and Ugnaughts, etc. Meanwhile the cases keep going out the door. So, yes, conceivably cases could arrive in a different order than the change was made in China, but that shouldn't be an issue, because a given figure, Leia for example, would continue to ship for the usual amount of time that a figure would have typically shipped, she just wouldn't be tied to a wave. Essentially the cases would be almost constantly changing, but the case ratios would always be an acceptable variety. They would replace "A" figures with "A" figures (Luke for Maul or Vader, etc.)
My general complaint isn't that there is too much of a delay between shipping, its that you can go months without seeing anything new, then they push out 3 waves in just over a month. By phasing in characters individually it would maintain interest for a longer term.
Frankly, I doubt Hasbro would adopt this model, as positive as this would be in maintaining an interest level at retail, I fear it wouldn't allow Hasbro the level of control they desire over the distribution chain. For example if a test showed an elevated level of lead after a product has been shipping, they would face an enormous logistic problem. So, I'm not going to hold my breath on this. I was more or less thinking out loud (even though I'm typing) about a solution that allows a more steady stream of things to find in stores. It just stinks that we've only seen 8 new Legacy figures since about Thanksgiving.....