Last year, Apple signed an exclusive agreement to use Liquidmetal — a high-strength metal that is light and can be processed like plastic — in their future products.

An ex Liquidmetal exec thought Apple would make iPhones out of it. A source speaking to MacTrast, though, says that Apple’s Liquidmetal investment won’t debut in the iOS line, but instead in March’s MacBook Pro refresh… which looks like a far more radical redesign than previously suspected.

Since Liquidmetal is both stronger and lighter than aluminum, a Liquidmetal MacBook Pro could be up to 20% lighter than current models. That means the 13-inch Pro will weigh only 3.7 pounds (down from 4.5),while the 15-inch will slim down to 4.6 pounds (from 5.8) and the 17-inch to 5.3 pounds (from 6.6).

Additionally, the report says that Apple has managed to improve battery life by up to 20% over current models, while simultaneously lowering power consumption thanks to a new type of display. Combined, this might drastically increase the already impressive battery life of the MacBook Pro line.

Hardware-wise, all MacBook Pros will be updated to Intel’s Sandy Bridge architecture, which we’ve heard before. All around, the new Pros will receive the higher-res, build-to-order displays of the current models as stock, bumping the 13-inch Pro to a base res of 1440 x 900 in both glossy and matte finish.

Intriguingly, though, the 15- and 17-inch models are said to be gaining a modular bay for the optical drive, which will allow it to be easily swapped with a secondary hard drive or other SATA device. Although MacTrast doesn’t specifically say so, this strongly implies ubiquitous SSDs to me, with users allowed to swap out an optical drive or larger external hard drive as needed.

Finally, MacTrast’s sources say the prices of the new MacBook Pros will be more aggressive than ever, with the 13-inch MacBook Pro starting at $1099, the 15-inch costing $1549 and the 17-inch starting at $2099.

This is the most exciting rumor we’ve seen about the new MacBook Pros yet. It’s a major revision of the current line. We have mixed feelings on the accuracy of the report — it seems too early in the partnership for Apple to be rolling out Liquidmetal in such quantities, for one; it’s a big jump from iPhone SIM ejection tool to a full laptop chassis — but a modular optical drive / HDD bay makes a lot of sense as a “missing link” mutation as Apple laptops evolve away from physical media and towards solid state flash memory.