Only last week, I was on CNBC saying that I didn't expect Costolo to be out until the end of the year. Sure, Costolo made a lot of mistakes and the management turmoil at Twitter was hard to ignore and hard to blame on anyone but the CEO. However, a number of recent management appointees were solid -- Anthony Noto is a great CFO, Kevin Weil is a great head of product and Adam Bain is a great head of sales.
I thought the board would give him until at least the end of the year to see how this new team performed, but Dick is gone.
If I had to handicap the possible successors for Twitter CEO (and I did successfully predict Satya Nadella would get the top job at Microsoft (MSFT) well before he did), I'd say the top outsider for the job would be Mike McCue of Flipboard. McCue used to be on Twitter's board until it was determined that there was too much competitive overlap between Twitter news and Flipboard news. His name came up a couple of weeks ago as a possible Costolo successor when it was rumored that Twitter might buy Flipboard.
As far as insiders go, though I love Noto as a CFO, there's no way he could lead a company like Twitter. With Noto coming over from Goldman Sachs (GS), there's a suit from Wall Street that would never be accepted by the product people and engineers of Twitter. It's really only Adam Bain's job to get, for an insider. Even though he's a money guy, he's been there five years and worked closely with Kevin Weil for years.