Someone earlier in the thread pointed out the choice of "product unveiling" (vs. "product announcement") in the phrasing of the tweet. Props to that person, sorry I didn't dig up your post and flag it as informative.
- unveiling not announcement (i.e. something already announced or at least teased, but thus far not revealed/unveiled)
- Tesla/SolarCity later, thus it's unlikely to be merger related, or consumer/business energy/power related
- it's not a capital raise or other financial move
- it's not hiring/firing unless they're revealing Tesla Employee 1.0 robots
Long before this tweet I had assumed the Model 3 unveil/reveal #2 would be in 2016 and ideally well before the Thanksgiving holidays so as not collide directly with the holiday activity and the flooded product announcement market for consumer eyeballs. Have it in October, at least a couple weeks before Halloween and the shopping march to Christmas and New Year's. Also, ideally you want all the fanatics to have everything memorized in time to have effective "socializing" of Tesla to friends and family over the holidays.
As such, I think it aligns with my previous expectations, phrasing of the tweet, and some current/popular predictions for it to be the following:
1. 2nd reveal/unveil of Model 3 including: (maybe) slightly updated nose, interior including instrument cluster + center screen
2. show off the new autopilot+autonomous capabilities are currently planned (but hopefully, please Elon!, not promising a date for autonomous yet... just AP improvements)
3. give us a taste of that cockpit/spaceship experience previously teased, probably including HUD
^ Rational guess
V Irrational guess
"Model 3 generation" seats that fold completely flat for napping while in autonomous mode, with adjustable pillow and alarm clock app for the main display.