After finishing a single-player game, I reviewed each of the statistics entries. Two of them caught my eye:
"Credits gained from the stock market"
"Credits spent on the stock market"
The AI players spend a decent amount of money on this!
I cannot find any "stock market" in the current in-game UI. More the point, a Google search, and a search of these forums, can find no reference to the stock market feature at all! No previews, press releases, forum questions, etc... did they just expose a new "mystery feature" in beta 3?