I think someone needs to come up with a good theory of what intelligence even is, then we can try to discover its mechanism(s).
1) Acting like a human (this is the Turing test approach)
2) Thinking like a human (this is cognitive science, and for now is focused on figuring out how humans think)
3) Thinking rationally, ie, following formal logic (the difficulty here is encoding all the information in the world as formal logic)
4) Acting rationally. That is, entities that react rationally to their goals (this one is notable because it allows fairly stupid entities).
These are all explained in more detail in Artificial Intelligence, a Modern Approach by Russell and Norvig
Another line for acting human would be the ability to self direct learning in a variety of situations in which a reasonably intelligent human can learn. That means a single algorithmic framework that can learn go, navigate a maze, solve Sudoku, carry on a conversation and decide which of those things to do at any given time. The key is that the go playing skill would need to be acquired without explicitly programming for go.
I believe a lot of our intelligence is the ability to perform solved AI problems given the situation. The key is combining those skills (whether as a single algorithm or a variety of algorithms with an arbiter) and the ability to intelligently direct focus. That's why most researchers aren't confusing alphago with general intelligence. It can play go - period.
Their attempt at a definition that synthesizes all the others is:
> Intelligence measures an agent's ability to achieve goals in a wide range of environments. - S. Legg and M. Hutter