So what's new with this revision? According to the folks at Leica, it's all about floating lenses:
The LEICA SUMMILUX-M 35 mm f/1.4 ASPH. differentiates itself from its predecessor by offering a floating element: the lenses behind the aperture blades are constructed as a floating group that changes its position relative to the front lens group during focusing.
In a nutshell, Leica is promising this setup will provide better imaging performance at closer focusing distances.
Leica is also including a metal, rectangular lens hood (pictured right). Asking price is $4,995 when it goes on sale in July. [Leica Rumors]