Yeah, it would be the first time he would flatly state something only to prove it false later. I don't think he would ever do that, even as a setup for a really nice surprise.
I also think that what will be revealed will be the Model S AWD plus the driver-assist technology, and that nothing else is on the menu. I believe the grave-digging remark is inconsequential, like others pointed out already.
The question is how advanced Tesla's driver-assist technology is, how exciting their demo will be, and how it will be received by the market. I don't care how the bots see it in the first 50 milliseconds, but how the humans react in the AH (if there's time left) and on Friday.
And the thing is, based on all the clues coming from Elon, in particular the one about the Internet missing "the magnitude" of the advance, I see a significant chance that this will be big. I don't see Elon organizing an exclusive event merely to announce things like lane departure and adaptive cruise control, or other stuff that competing sedans have had for years. Automated highway driving is a possibility, even though it sounds mighty ambitious, but what ever it is, it must be a first, and it must be significant enough to make it the highlight of the evening. It would also be in line with his many previous references to automated driving technology being closer than people think, the large numbers of engineers they hired in the field, and his comment on the earnings call about R&D expenses being much better than they look because they are not showing all their cards.
If this is about automated driving, the market should reward it. Adam Jonas used the prospects of this technology as a reason to put the brakes on the stock, but if Tesla is proving to be the leader in this field too, then consistency demands that the stock should rise. Because, of course, the markets are always consistent and rational...
Anyway, I'm placing my bets on the assumption that this is one of the cards up their sleeve, and it's an ace.