My guess is that a Wilson higher up made the decision to sell one of the molds that Dimitrov was playing with early, when it seemed as if that was a keeper. Production lines start to rev up, and out of nowhere Dimitrov's team sends an email sends a message to the engineering department detailing what changes he wants made to the racket, including the box beam.
At this point, they've got 8,000 units produced early in production, their assembly lines are already working on the next batch, maybe the single production run has another 32,000 units to go.
Do they eat the loss on the 8,000 units, the raw materials, and the labor that's gone towards setting the molds just to put a slightly different racket on the market? Or do they just make a separate mold and use it for limited production runs and keep selling the racket that they had already decided on?
My guess is that this generation of prostaff rackets will be the retail flat beam that we're familiar with, and within two years when the next generation of Wilson rackets is released, they'll release the box beam version and call it an update.