Here is the puzzle: It's not a product, but a technology. And it's unexpected. What might it be?
Elon Musk's tweet from Sunday confirms that there will be no new product unveilings in the near future: "Cybertruck is our last product unveil for a while", which is reasonable as besides the Model S, Model X and Model 3, Tesla has 4 models in the pipeline:
At the same time, Elon hints at upcoming "technology announcements", which mostly will be unexpected:
"Cybertruck is our last product unveil for a while, but there will be some (mostly) unexpected technology announcements next year"
We already know that Tesla is working on its own in-house battery cell technology that would provide higher energy density/more affordable prices, which is not an unexpected then.
The question is what else does Tesla have on its shelves that we mostly do not expect?