Lemme Elaborate on:
Groups with different resolutions per monitor so long as they match along the group's interior edges. PLP and 1920 x different are likely the common cases. Using 3@ x1200 in the top of a 3x2 and 3@ x1080 in the bottom would get the crosshairs out of the bezel. Portrait mode should also support mixing 16:9 with 16:10.
Basically if you can make it a Rectangle / Square, it'll work in eyefinity.
This would be useful for a whole host of configurations:
1600x1200 + 1920x1200 + 1600x1200
1200x1600 + 2560x1600 + 1200x1600
There are more, but I don't care to elaborate on this. Either way, Eyefinity has the potential to be flexible, this generation, it probably wont happen, but the next generation of cards should be.
Also, It should matter if it breaks the 8192 pixel barrier for DX9, there is DX11 out now, and some games can pass the limit even in DX9. Have the user deal with those incompatibilities. We don't need a guiding hand. (same argument goes with Bezel Compensation).