Nvidia probably won't allow anything on non-nvidia chipset unless Intel agreed to include at least one core logic on the system. Basically X38 with Nvidia mcp on the same board just like what we see on skulltrail previously showed on IDF. Apparently, there is no technical reason why X38 cannot support SLI on its on without nvidia MCP. It is more on the Nvidia side to say yay or nay.
The initial release of X38 based motherboard with no official SLI support. The later version of it which include nforce mcp that will support SLI.