Here are Warren’s proposals from that article:

(1) Shift the legal foundation of corporate purpose from solely being focused on maximizing shareholder value to allow other goals as well. This model has problems from a capitalist business standpoint (https://hbr.org/2017/05/managing-for-the-long-term#the-error-at-the-heart-of-corporate-leadership). It also has problems from a societal standpoint as highlighted in the book The Golden Passport. Politicians aren’t talking about this issue and there is a current problem with it.

(2) A Place for Workers on Corporate Boards: As has been pointed out below, Germany does this without affecting economic productivity. Workers are a major part of the system. Their stakes shouldn’t be ignored or at best nonexistent at the table.

(3) Limits on corporations ability to engage in political speech. There is a definite tension here of forced speech. Kennedy dismissed this in Citizens United, but the same normative principle led the Court to its union speech decision in Janus. I don’t think this is a bad idea.

To address your points more head-on, I think you are falling into the incremental step fallacy. I agree this is unlikely to be passed in 2020. But a political idea, of cultural change, has to start somewhere. Just because it requires time doesn’t mean we can dismiss it entirely.

In regards to your legal argument, I agree and disagree. The current conservative Supreme Court will make things difficult. But I think they are 100% wrong on this. The corporate form is surely not required by any originalism, and is based entirely on normative arguments that have accelerated in recent years. A more liberal court (again a long term goal) could change this.

I am not sure what you mean by huge new agencies or a government enforced pay cap. Rather this is a decision to change the structural way that corporations function. The government created corporations, they can place limitations on how those corporations work