The rumors around him are growing, which may be a good sign. At the end of October, it was said that he would be ready to go into production. Now, about 15 days later, the DigiTimes says that the components for the production of Apple's new ultra-thin notebook will start shipping this month, the 15-inch MacBook Air (or Pro) would start to be shipped in mass from March 2012.
Particularly, I believe that this is a new MacBook Air, and not a MacBook Pro. If this is really a professional notebook, it could cause some confusion for the general public, since the new machine would be equipped with SSD instead of HDD, it would come without optical drive In short, all the features of a MacBook Air, but with a 15 inch screen.
I imagine that the confusion would be the same generated at the time when the company started selling MacBooks with an aluminum housing (late 2008), being difficult for lay customers to distinguish the difference between the "normal" laptop and the professional of Ma. Little then Apple again offered plastic MacBooks, differentiating the models again.
I think the same applies here: of course, the MacBook Pro will sooner or later gain the Air's features (SSD, ultra-thin, no optical drive). In return, Apple will have to offer a more powerful graphics card, more disk space for storage, more RAM (up to 8GB), and it seems to me that this is not the case with this rumored 15-inch machine.