I'm just going to point out how unrealistic players being able to have any significant say on the internal maters of a mega corp through a shareholder vote would be. Given how large many of the mega corps (like ship manufacturers) are in ED, players being able to buy stock for any mega corp would have virtually zero impact on the mega corps in question.
Using Faulcon Delacy as an example, think of how many Anacondas are owned by players (INARA says that this figure is just under 64000). Assuming that Faulcon Delacy only makes 25% profit on each Anaconda sold (full price, discounts are done by the individual retailer), they have made 2.27 trillion credits by selling only the Anaconda, only to players with INARA, and only in the last 5 years. For reference, canonically the buying power of 1 CR in the ED universe is roughly equal to $50 US, meaning that 2.27 trillion credits over 5 years is about 22.7 trillion USD per year, which is roughly equal to the GDP of the United States of America.
Now, considering that Faulcon Delacy presumably makes more than 25% profit per unit sold, the Anaconda is not the only ship they sell (INARA says players own ~62000 Pythons, ~56000 Sidewinders, ~42000 Cobra IIIs, and ~35000 Krait IIs), not every player uses INARA (~37000 players use INARA despite several million copies of ED having been sold), players only make up a fraction of the in-universe market for spaceships, and the companies like Faulcon Delacy have existed for hundreds of years, the net worth of these companies FAR outstrips the players' ability to buy enough of their stock to have anything close to a controlling presence in a shareholder vote. Assuming that Faulcon Delacy makes 50% profit per unit sold on the aforementioned ships, INARA statistics are representative of the 1.3 million people who bought Horizons, the ratio of players with INARA to players without INARA is equal the ratio of players to NPCs, and that Faulcon Delacy is seeing fairly aggressive growth of 10% per year, that puts the net worth of Faulcon Delacy at 17 quadrillion (1015) credits.
Essentially, in order for players to own all Faulcon Delacy's stock, each of the 1.3 million players who own Horizons would need to buy 13.2 billion credits of Faulcon Delacy stock. To make matters worse, this is a conservative estimate (it does not include the Viper III or IV, Cobra IV, Krait Phantom, the 1.7 million players who only own the base copy of the game, accounts that have been reset, that the ratio of NPCs to players is going to be closer to 340:1 or 3400:1 than than 34:1, or that Faulcon Delacy might have a growth rate similar to that of a banking institution), and the playerbase would still be hard pressed to be able to buy out half of the stock for a single ship manufacturer. If we try to come up with a more accurate estimate, but only use a NPC to player ratio of 340:1 and give Faulcon Delacy a growth rate of 3% per year, that gives us a net worth of 557 quadrillion (1015) credits, which is well beyond the collective purchasing power of the playerbase and is still probably at least 1 order of magnitude too small.
TL;DR: Mega corps have absolutely ridiculous net values and the collective purchasing power of the playerbase doesn't have even the slimmest chance of buying one.