I don't think forcing majority stakeholders to sell their stocks over the years would have your proposed effect. The position of power here is mostly with the CEO of those companies. And that's not gonna change with this scheme.

Honestly, there isn't a clean solution to this problem- or at least none that doesn't come with unpredictable consequences. I think everyone can agree that companies growing too large inevitably become harmful for the society they're enabled by, but there are no previously established solution we can reach for... And every decision you can make will have trade-offs. Also, were pretty late game into free market capitalism. Any changes to the status quo will dis-/advantage someone, and they will utilize the tools available to them to stop you. So such deep cutting changes are beyond unlikely without first descending into complete chaos. Which would likely be worse for the majority of people...