I love that there are over 200 posts trying to figure out the meaning behind one tweet!
Having said that, usually folks on TMC are able to figure out pretty quickly what an announcement is about (such as MT COTY), or at least narrow down the viable options. The interesting thing here is that it doesn't seem like there's a really good guess, other than something to do with superchargers.
I have no better guess than anyone else. I would make the following observations -- putting ones "money where his mouth is" is a figure of speech. This involves something that Elon has mentioned in the past, and probably on multiple occasions. Could it be the viability/practicality of the SC network, or the financial security of TM? The problem with the former is I'm not sure where his personal investment, or "money" (and here I don't think he means cash, for those who were speculating how liquid Elon is) would come into play with that. This is something that TM should be doing as a business because the CEO has already said so. Accelerating the pace or scope of the SC network doesn't seem worthy of that kind of tweet -- he already has put his money where is mouth is on this topic when he made the SC announcement a few months ago. The problem with the latter is that I haven't heard Elon saying too much about Tesla's financial security, other than talking about how hairy things were in 2009 before they got the gov't loan approved and the investments from Toyota and Daimler. It's not like TM is wheezing along desperate for free cash flow, so what would be the point of a personal stock purchase by him or a personal repayment of the gov't loan?
The implication of putting his "money" on the line is taking some sort of personal (financial) risk or stake in something related to TM. This is unusual because as a public company with a fairly healthy share price and access to other funds means that there's not much TM isn't able to do from an investment perspective as a business that would necessitate Elon personally putting his money where his mouth is. This is why the SC network doesn't seem the right fit.
Anyway, it's easy for me to shoot down all of the speculation so far as not fitting the bill, but that doesn't leave me any closer to figuring out what the announcement is going to be next week. My focus is on looking for something that Elon has been fairly vocal about, because the implication of his tweet is he's going to more than just talk about something he's mentioned before related to TM, and put some personal financial stake behind his idea or theory.