i really hope you are right and they do have a thinner/lighter design. once the mac mini got the odd dropped, i had no reason to doubt that apple would also drop the odd on their macbooks.
I can see another scenario. In the past Apple has been hesitant to add too much choice to their lineup. Considering the number of people buying Macs, that made a lot of sense. Today there are a lot more people interested in these computers, making it plausible to expand the lineup a little bit.
Here's the scenario:
Portables:
MacBook Air: 11" & 13". Same wedge design, eventually getting thinner. Upgraded internals, integrated GPU, retina display
MacBook: 15" to start, perhaps adding 13" later. As thin as the Air at it's thickest point. No ODD, FW800, Ethernet-but has dedicated GPU, fast processor, SSD, retina display, built in RAM. Marketed as the full-powered notebook of choice for consumers.
MacBook Pro: 15", maybe 17". Upgraded internals, retina display, retains legacy ports. Configurable 'til you're blue in the face.
Desktops:
Mac Mini: Retains same design, upgraded internally as tech allows. Ivy Bridge will support retina display monitors.
iMac: Possible thinner, chinless redesign. Retina display, Ditches legacy ports, maybe retains ethernet. Marketed as the desktop of choice for consumers.
Mac Pro: Probably retains existing design, internals upgraded appropriately, retains legacy ports. All GPU options support retina resolutions. Configurable 'til you're blue in the face.
It used to be a desktop and a portable for consumers, and a desktop and a portable for pros. The market has changed, the "Prosumer" is now a major force in the market and Apple's market share has grown to the point that it can offer some choice. They understand that pros are less concerned with having the flashiest toys and are more concerned with all their stuff continuing to work. They also know that they can't just abandon that market, there's a lot of value in the fact that creative professionals choose Macs, it's a hell of an endorsement. Doing it this way would allow for innovation on the consumer front, while not alienating pros.
...Or maybe it's 2:30 AM and I need some sleep.