In my understanding, a PBC is effectively the same as a for-profit company with regards to these sorts of things. Unlike a non-profit, a PBC has stock, which it can sell, so that's how it would get acquired. I believe that there were even some PBC SPACs back when that was fashionable.
> If they violate their charter as Ello may have, who exactly enforces it or file a lawsuit, and what is their compensation?
The only real thing a PBC does is change "shall maximize shareholder value" to "shall be managed in a manner that balances the stockholders’ pecuniary interests, the best interests of those materially affected by the corporation’s conduct, and the public benefit or public benefits identified in its certificate of incorporation." See here for Delaware: https://delcode.delaware.gov/title8/c001/sc15/
So it would look like any other shareholder grievance against management in form.
> Benefit corporations are neither nonprofits nor hybrid nonprofits. Benefit corporations are for-profit corporations that need to consider stakeholders, morals, or missions in addition to making a profit for their shareholders. Nonprofits can't be benefit corporations, but they may create one. Due to the public benefit purpose provisions, expanded fiduciary duties of administrators, and extra shareholder rights created within the model benefit corporation laws, this structure may be helpful to operate and scale the earned-income activities of a nonprofit.
There are only two fiduciary duties in this context: the duty of loyalty and the duty of care. A director of a corporation owes no fiduciary duty to maximize shareholder value.