Interesting thought experiment. While there is no inherent reason a company's stock couldn't be used as a currency like in Steemit, for it to be valuable in the wider world it would need to be listed on a stock exchange, and stock exchange rules and well as regulation of public companies would generally make this system impossible.
Yes, agreed there. But the main reason for this thought experiment is really to see if there's something of comparable value, not whether it is practical to make this system :) . In this scenario, I would also imagine the stock wouldn't be used as a currency at all, and it would be purely treated as equity.