From the EVGA board in a different topic, discussing why bios P05 for the 780i board disables SLI memory for anything more than 2 DIMMs (all previous bios versions allowed a person to enable 4 DIMMS with SLI.....it's no longer an option for P05).
It is possible for the board to override the restrictions set in place by the memory's EPP settings. Under normal circumstances (and with most boards), the memory itself won't allow you to enable SLI if you're running 4 sticks of RAM because the EPP profiles aren't IDENTICAL. As we all know, the motherboard can override this, however it can cause problems because the memory isn't tested to it's full specifications in 4-stick configurations (because of the extra load on the bus). This is why it's recommended to use the least amount of memory modules as possible (EG: 2x2gb instead of 4x1gb), because stability is a huge concern.
Regardless, I'm going to try and find out if this was an intended change or something that might be re-enabled in the future. Though keep in mind, if it's an intended change, then the above reason is why. And memory manufacturers also back the claim of memory tested in 2-stick configurations, and not 4. A few companies sell 4-stick kits which are tested to run at their rated speeds (usually 8gb and 16gb kits).
It's also important that note that SLI-Ready is nothing more than a RAM self-configurator, and as others have mentioned, you can achieve the same level of performance/stability by setting the RAM manually to whatever the RAM manufacturer recommends.