We'll be using scatter mostly for DOF and motion-blur initially, both being algos where you can cache the few nearby lines or tiles of the frame-buffer and upload on cache contention. Plus, the problem with 100 shaders scattering to the same pixel can be solved initially via a round-robin cache-update using 1 ALU (can do both addition and alpha-blending), and in the future - by having tiles of cached additives, later added together in a pyramid fashion (can do only addition). SLI will be problematic with scatter, but possible at the price of some performance - or well, with improved performance when each card keeps in GDDR the scatter values for the other card's scanlines (can do only addition).