"Really exciting @TeslaMotors announcement coming on Thursday. Am going to put my money where my mouth is in v major way."
Most realistic suggestions so far don't seem to fit the twitter text. They either aren't "really exciting", or not something that would make Elon talk about investing money (that's not already invested).
I can't make up my mind about a guess.
- It seems early for Gen III announcement, especially for already having a prototype. Except for recent twitter activity, there are no rumors about first specs or so.
- Can't think of any possible larger Model S related announcement that would fit above description.
- Supercharger plans already exist going far beyond the current state. They might get accelerated, but that seems difficult to convey in an announcement.
- There are no rumors about new battery technology ready to be used in production, or any other pending innovation.
Out of these, an official Gen III announcement is perhaps the best fit. With an official name, and just a few more specs in addition to $30k+inflation, 200+ miles, smaller than Model S yet otherwise similar, with more features optional instead of standard. However, "best fit" doesn't necessarily mean "very likely".