But I also don't think that this will bring the singularity because of the complexity limits mentioned above. Strong AI will speed up some cognitive tasks with compound interest - but only until the physical feedback level is reached. Or a social feedback level is reached if AI should be designed to be so.

Depends what you mean by "singularity" and, to some extent, "AI." If "artificial general intelligence" means it can do any task a human can, at minimum you've just taken away labor supply as a constraint on economic growth, so now the economy can more or less grow as fast as we can build new hardware. Robin Hanson (an economist) has predict that would lead to the economy doubling in size every month or so. Which isn't as fast of a rate of change as Eliezer is predicting, but still arguably deserves the label "singularity."