I'm not even that optimistic about 'success'. It's actually feels a little weird how much my thinking on AI has changed. A few years ago a digital toddler might have seemed like a sensible approach.
What seems nonsensible about it now? (I presume you're meaning in the sense of even succeeding at the AGI goal, not in the sense of succeeding in the Friendliness goal.)
http://multiverseaccordingtoben.blogspot.com/2010/10/what-would-it-take-to-move-rapidly.html