I see AWD and Standard Range as two separate options that will become selectable in the design studio. Imagine a checkbox that says AWD. They will add that in Mid-2018. What does this say about short range vs long range? Nothing. That's a different checkbox that will be added later. Therefore, the way I read it, Mid-2018 for AWD means only LRD.
In this scenario, SRD would be a selectable option as soon as SR becomes available. You would just select the SR checkbox and the AWD checkbox and there you have your SRD. However, they might make the SRD available before SR because of higher gross margins. They need to show that the Model 3 situation looks good before raising more money for the Model Y. Tesla seems to be more focused on the Model Y than I would've thought they would be at this stage.