SAG and the WGA
Eventually the studios and the WGA will make a deal. Will SAG accept the WGA deal as a template (assuming it doesn't accept the DGA deal as a template)? The conventional wisdom is yes, but the question's still worth asking.
Also, there's at least one issue that's important to SAG, but not to the WGA or DGA: forced endorsements. These are products placements taken to the next level: instead of just seeing a can of Coke in the scene, we see the actor comment on it ("what a great Coke that was") and/or handle it (i.e., drink it).
These practices are considered forced endorsements because the actor is required by the script to in effect endorse the product. That means he or she can't realistically do a commercial for a competitor, such as Pepsi. Nor is Coke as likely to hire him to do a commercial why bother, since he just did one for free, as part of the program (which means that the audience is much less likely to skip it than an actual commercial).
So, SAG wants additional payments for forced endorsements. By contrast, the WGA's only looking for consultation between the producer and writer when a forced endorsement in written into a script; it dropped earlier demands for additional compensation.
SAG and the WGA are probably collaborating pretty closely behind the scenes on their evaluation of the DGA deal. I can't imagine forced endorsements would be a dealbreaker.