All technology revolutions need a breakthrough in three factors to succeed: energy, transport and communications (see Jeremy Rifkin’s work on this). The most plausible argument against AI reaching overall human-like capabilities could be energy availability. I don’t think we have the energy system required to accommodate such a massive explosion of AI. Organic systems, like the human brain, are still the most energy efficient systems present.
However, we, humans are flawed by nature. And this is good. I think limited intellectual capability exists for a reason. The fact that there is some kind of natural upper limit to human IQ/intelligence is an essential requirement for our survival as species: any system needs an OFF switch (natural or artificial) as part of its in-built safety design. Therefore, we may never reach Singularity, or we may reach an adverse form of Singularity, which in the process of optimization to reach its perfection state, self-destroys.
For all we know, this might have happened already in the past. The energy requirements to carry on the task of optimization are so large that this intensity creates a black hole which sucks in not only the Earth but also the whole Solar System. The only way humans are able to survive such a scenario event is to exit the Solar System just before the process of self-destruction. It must be humans, in organic form, exiting, for they must make sure that they preserve their imperfections as the only hope for future survival (a perfect trans-human or an AI-equipped machine would simply carry on with the process of optimization and eventually reach a similar event).
With the knowledge on hand, these humans do not search for a habitable planet but simply create a biosphere on the first available planet they encounter. Then they proceed to recreate our world – the proverbial Garden of Eden – under one main condition: “never bite from the tree of knowledge” for fear of a repeat of the above scenario again. And again, and again, the process keeps repeating itself…
The universe, therefore, has to be expanding all the time because, if not, these black hole explosions will eventually destroy it all. In other words, humans are just planet-hopping imperfect organic forms who, in search of perfection, leave nothing but black holes behind them. Long live the pessimists!