Can't really expect any kind of range update to the Model S until Tesla has their 2170 cell production sorted out (i.e. solves the problems at the Gigafactory). And even then, you have to heavily ramp up Model 3 production first, or investors will run for the hills (the Model 3 uses 2170 cells).
So I'd give it at least 6 months. And in the end, only Elon and his inner circle know for sure.
(If it makes you feel any better, I'm waiting for a refresh/update before I buy, so I'm more on pins and needles about this than anyone).
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