So far, NVidia was refusing to license out SLI to other motherboard manufacturers and/or competitors. NVidia wanted to be the only one to offer its technology, associating specific chipset to the simultaneous use of two or more NVidia graphic cards. However, the future Intel chipset X58 should be natively compatible with SLI.
While Intel will have to have its chipset certified by NVidia, it should not be a problem. This was part of the deal for NVidia to obtain license for Nehalem-compatible chipset. For NVidia it is also a way to further promote CUDA as performance gain will be even higher if SLI. If we finally get optimized drivers, there should not be any hardware issues for us to get SLI in our future Xeon Nehalem-powered Mac Pro.
[translation by Linathael]