There's still an agency problem between the shareholders and board members, but at least the shareholder votes will be weighted for the long haul. Locked shares would have to be held in a way that prevents wrapping them in a salable derivative.
This would have a significant impact on encouraging long-term investing for investors and long-term planning for companies.
This should apply only to shares in individual companies and not index funds or mutual funds.
It would also encourage a shift away from short-term speculation and to long-term investing in great companies.
Where I live stocks profits are taxed at 20% at first, then 5% less for each 5 years you hold them, down to 0 taxation after 20 years.
Also, this kind of progressive tax reduction should only apply after the company is public. So the clock for VCs, founders, etc only starts at the time of the IPO.
This would ensure all the early stakeholders are also aligned in investing in the long-term success of the business.
Currently, these early stakeholders are more likely to be focused on cashing out and having a liquidity event.