It would appear that Apple is already lining up a new notebook for their Mac range and that this new entry in the range is already in the late testing phases.
Mac Rumors learned of the device, though as would be expected, actual information about the product is difficult to find. At present, it is unclear whether the device will be marketed as an Air or a Pro in the MacBook field. It was only recently that Apple updated and refreshed the MacBook Air range, dropping the price, and removing the original base MacBook from the future Apple line-up.
In either case, the new system offers a 15-inch screen and a thinner design. The MacBook Air series has been noticeably thinner due to its lack of an optical drive, as well as its usage of an SSD in place of a traditional hard disk. If the MacBook Pro was to go down the same route then it is more than likely it would be able to enter the "ultra-thin" market, as it has been known. This market looks like it will be growing more popular, as the so-called "Ultrabooks" could be releasing as soon as September, to steal some of Apples thunder.
In addition to the 15" model that is appearing on the internet it seems that 17" models are also in the works. As Apple updated the MacBook Pro line-up in February 2011, these new devices could be released close to the end of the year, or at the start of 2012. Apple has recently started holding Mac-related events in October during previous years, so it is possible that they will announce these devices at this event.