Apple is planning a radical redesign of the MacBook "soon," if a forum post out of China is to be believed.
A key aspect of the redesign would be the elimination of the fan assembly, according to MacRumors, which describes the post as coming from a reliable leaker of future Apple hardware.
A fanless design almost always implies ultra-thin and light. For example, the iPad Air is a fanless design as are Android and most Windows tablets. Even some of the newest, thinnest Windows 2-in-1s, such as the Intel Haswell processor-based HP Spectre 13 tablet that can double as a laptop, are fanless.
(See Imagining a newfangled MacBook)
The post also mentions that the new MacBook would have a trackpad sans mechanical button. Microsoft's Type Cover ultra-thin keyboard that goes with Surface Pro 2 and Surface 2 has that kind of trackpad.
This latest rumor follows an NPD DisplaySearch report last October that forecast a 12-inch MacBook with a Retina-class display. That report said simply that it was due in 2014.
To date, the MacBook Air has come in two sizes: 11.6- and 13.3-inch -- both with relatively low-resolution displays.
Whatever Apple ultimately decides, it seems certain that the ultraportable laptop will eventually get a physical makeover. The MacBook Air hasn't seen a physical redesign or display change since late 2010, when Apple introduced a new chassis and debuted the 11.6-inch Air.