Very intriguing arguments. Your second paragraph is very true and profound indeed.
First I must ask, where does this assumption that Autistics do not have empathy come from?
Secondly, to play a little devil's advocate and start a little controversy... To contend with your first argument, Hitler and Osama Bin Laden had empathy for the people they fought for. And speaking of Christian corruption. What about the crusades? Even earlier, the Romans demonstrated a twisted sense of empathy towards the Jewish leaders when they decided to crucify Jesus. My point is only that your argument can go both ways, to save or damn. I see it more as a balance, than what pushes more towards survival or extinction. Now I am being pedantic and arguing semantics (I promise I am not intentionally being condescending, if I come across as much in saying...) but empathy and compassion are not the same thing. (I think I might've even confused the two in my earlier argument....).
The right traits definitely helped mankind. Of those traits, I believe that intelligence is a key player amongst those traits. Hence a 67% percent increase in the cognitive functional part of the brain equates to the
potential superior intelligence. Trial and error is an apt description of evolution. And within the hypothetical context of Autism as the next evolutionary step, this is why some thrive better and some struggle. It is not simply an overnight process. It could still take hundreds of years to perfect.
I think when I say Autistic, the vision that comes to mind are those that appear (forgive my insensitivity) retarded - rocking, hand-flapping, drooling, uncoordinated movements, screaming, tantrums, gibberish, etc. There are "high functioning Autistics" or Asperger's syndrome. Most of these individuals are of average to genius level intelligences.
Perhaps in the survival of the fittest sense of evolution, my theory falls short (though I'm not quite ready to yet give it up). Who knows what man went through during other stages of evolution? Maybe they simply threw their evolutionary babies over a cliff thinking them to be "retarded" or some such. Who is man to decide natural selection? Perhaps it took a little creativity and a mother's unfailing love and loyalty to her offspring to help them succeed.
Sidenote: It almost seems irrational to rationalize that natural selection uses logic to predispose evolutionary progression.
But as you said, evolution is not linear. What if the evolutionary progress is setting up a new 'race' of human beings. An improved thinking type? Again, a near 70% increase in brain neurons in the area of the brain responsible for conscious thinking suggests that this creates
potential for superior thinking capabilities. Without given the environment, skills, and support to reach this potential, clearly they will fail. Some succeed despite this, those with Asperger's.
The CDC reports that 1 in 88 children are diagnosed with Autism. These are just the ones they catch. The CDC has reports where they found some autistics that slipped through the system. In any case, these numbers are in regards to the more obvious cases. Again, what about those with Asperger's? They appear normal as any other child, reaching all the key developmental milestones as any other child does, but have their own unique set of challenges that are more prominent in teen/adult stages. How many were not diagnosed (or even misdiagnosed with other disorders)?
Your final paragraph is interesting. How does evolution occur if it requires those of the next evolutionary step to procreate those of that evolutionary step? At least this is the question I have assuming that you mean that it would require Autistic people to reproduce to create more "Autistic" people (in the context of evolutionary progress).
As for famous Autistics...
It is rumoured that Albert Einstein, Mozart, Sir Isaac Newton, and others may have been diagnosed on the Autism Spectrum had such a diagnosis existed in their times.
http://www.toptenz.net/top-10-autistics-known-today.php
http://autismmythbusters.com/general-public/famous-autistic-people/