The shorts have been short
The shorts have been short for a long time, most of which was during the last couple of years where there was extreme doubt that the Model S would even reach production, or would end up hopelessly compromised by price increases or downgrades in quality.
Much of that analysis has already proven wrong, the foremost of which is that the Model S is in production and about to be delivered. The prices are set and are fairly competitive at the various trim levels vs equivalent gas powered cars. We already have government ratings on safety and electric range, which are two critical metrics, both of which are extremely attractive.
The only remaining doubt is about actual performance and build quality. And anyone who thinks that Goldman Sachs doesn't have solid reports about the first production models is smoking something.
The car looks awesome, and there are extremely good reasons from a basic physics standpoint to think the car has gangbusters performance. This is completely aside from the fact that Tesla is already the most experienced producer of high performance electric drive trains (See Roadster) in the world.
So unless the state of the art Tesla production line manages to put out cars with terrible quality (fat chance with that bet), the only hope of the shorts at this point is that customers will refuse to buy one of the best looking and performing cars in the world, simply because you have to plug it in at night.
The shorts look to get burned badly on this one absent a major negative media effort by Fox News.