I think the reason SLI is dead is because the manufacturers saw where the technology was headed. AMD is about to make it irrelevant and you can bet Nvidia is working the idea and will have something similar soon thereafter.
AMD’s next GPU will have multiple chips built into it. Essentially it will have 2 GPU’s merged into one card. The biggest benefit is that no software will need to be written specially to take advantage of it like is needed for SLI. AMD already introduced this with their chips using the “infinity fabric” technology to connect multiple CPU’s, and a similar technology will do the same for GPU’s.
This will be huge for the future just like we have CPU’s with many many cores the same will happen for GPU’s thus eliminating the need for SLI.