I would be surprised and disappointed if they did not literally drive a Model 3 onto the stage. You cannot state "reservations are open" when you don't show people the car. Keep in mind the engineering power (both in experience and numbers) of Tesla is far better than when they were developing the Model X. They got a Model X onto the stage in 2012 with people riding inside of it, and the prototype falcon wings worked well too. Sure it took 4 more years to actually produce the X. My prediction is that the Model 3 will be shockingly on time for both the reveal and production, since Tesla has far stronger engineering, manufacturing, development, software, supply chain, drive motors, and battery supply/technology than it did for the S and X. If the Model 3 is based on the overall shape and engineering of the Model S with no bells and whistles, then it will be a runaway success. For the Model 3 reveal, it would be very disappointing if there was only a render or a non-drivable shell.
On a side note... let's change up the discussion a bit. We've forgotten to put some focus on Tesla Energy. There have been photos of many Tesla Energy crates from all around the world. Word is the Gigafactory is ahead of schedule and producing product for both Tesla Motors as well as Energy customers (mainly on the utility level). Even here in Alberta Canada, one of our largest utilities (oddly enough partnered with Buffett and co, of NV Energy anti-solar panel fame) has Tesla Energy battery project(s). How much do you people will this affect the upcoming earnings as well as the forward guidance? What is the profit margin on these battery products?