Refreshing the interior is unlikely. The car is 6 model years old already 2013-2018 with a few 2012s thrown in too.
Since it's tesla maybe they'll take a little longer but 6 years is about it in the car world before a new model is deployed.
The facelift kicked in after what...4 years? So maybe that will drag this out to 2019 but in either 2019 or 2020 there will be a whole new model S.
People get bored even if something is great. Most people who bought a 2013 model S, then upgraded to a P90D in 2016 aren't going to buy a 2019 P100D if it's largely the same car they've owned twice already. I would. I think it's great. But I'm not most people.