It's an interesting question. 

Let's start with who doesn't run Twitter. 

1. It's not Evan Williams who just left the company. And this time it feels like it's for real. 

2. It's not the CEO, because they just brought back another founder, Jack Dorsey, to run the product. What kind of CEO isn't in charge of the product? Esp a company with exactly one product. Maybe if they were a diverse conglomerate you could find a way to run it without running product. But this is not a diverse company. 

3. Is it Jack? Doesn't seem like it could be. If so, is he really committed to Twitter? He's only a part-time product guy, with another company he's CEO of. He probably wouldn't be a great choice for CEO either. Nice guy, but running a 350-person company with millions of users is pretty hard stuff. 

4. The board? My guess is yes, they probably are actually making the executive decisions for the company. But it's just a guess.  

What do you think?