(I work at OpenAI.)
The board of OpenAI Nonprofit retains full control. Investors don't get a vote. Some investors may be on the board, but: (a) only a minority of the board are allowed to have a stake in OpenAI LP, and (b) anyone with a stake can't vote in decisions that may conflict with the mission: https://openai.com/blog/openai-lp/#themissioncomesfirst
Will never work in practice