It is a mini-game at best, and a money cheat at worst.
The Stock Market is a complex and intricate system in the real world and we would need one that was almost as complex and volatile to make it usable ICly. Given that people can get huge boons of money and be willing to risk it ALL in the IC world, with very little repercussions if they were to lose it, it just doesn't seem viable at this point.
We're considering some alternatives that still keep it in the realm of 'something that happens ambiently'. Like maybe your Grid 3.0 tools are able to 'mine' stuff like the modern day bitcoin does, and you get some income off of that, but generally speaking, I don't think the stock market is going to happen any time soon.
In 2103 all transactions would be done via AI designed specifically for the purpose and there would be huge barriers to entry for private citizens to get involved. The cost of shares in mega-corps would be prohibitively high and result in a secondary market where you buy pieces of a share, like an index fund-- while I like stocks and funds and all that, I just don't know that the time investment this would take is worth it.
I'm open to hearing arguments to the contrary but at this point we have no plans to bring it into the IC world in a way player characters can interact with.