Until the backorders are filled and certain manufacturing requirements are met, no more models will be introduced. There are a bunch of test mules, but nothing that will be called "future product" yet. If you 'wait' for a .45c, you may be waiting a while.
Realize that S&W is VERY serious about going after the military contract with the M&P45 and they will need to be able to mass produce that pistol in record numbers to fill it. Several hurdles still exist in the plant to allow that and these are top priority, not introducing another model.
Heard that from the VP of production himself only a few weeks ago.
And no he didn't go into details as to exactly what production issues exist. All he would say was that the goal was to eliminate all hand fitting so that the pistols could be assembled from boxes of parts.