It seems like C-level executives in the tech. industry are just passed around like tired, worn cards. It's like bad re-gifting. They need to promote more internally to C-level.
In the transformation toward maturity they can engage in promoting leadership from within with guidance from acquired leadership.
Not all companies have needed that external experience, but many have.
I'm guessing that within 12 months Jack will not be a part of Twitter nor any other tech company.
Interesting thought, especially considering the relative success both of his companies have had in the prior 12 months (in the stock market, anyway)