I highly doubt they would take a deferral approach for any option they plan to release with, delays or not.
If you're going to use the Model X as a comparison, look no further than the 5 seat option. When the Model X opened to the first configurations (after Founder/Signature) it had a 5 seat option that could be selected. It just had the message "available mid 2016" (this was late 2015).
Just like AWD for the 3, Tesla communicated prior to release that a 5 seat option would be available for the X. They had it available for people to select when orders opened, but didn't fulfill the option until later. I see no reason to believe they would do anything different for the 3.