Some counterpoints:
Behavioural modernity without common cause like language, and without any definite characteristics that weren't present earlier in some form is far less plausible, and pretty much falls apart.
Migration out of Africa is dated at anywhere between 125kya and 60kya, not 50kya.
Even starting count at 60kya, agriculture being invested 10kya multiple times independently is still extremely surprising.
Even disregarding admixtures with Neanderthals, Denisovans etc. most recent common ancestor is more like 140kya-200kya by mitochondrial and Y chromosome dating. Dating anything here is very dubious, so you can find a number that fits your hypothesis whatever your hypothesis might be.
At each point of history vast majority of humans lived in places very far from those covered by ice, or particularly cold. Agriculture was invented only in places far from ice. These are still climatic effects like rainfall that depend on glaciations, but these are much more tenuous links.
Modern attempts at domesticating plants and animals show it takes a few decades, not tens of thousands of years. Now these are done with benefit of modern science and technology, but still it doesn't imply tens of thousands of years.
Well, we know pretty well that even when societies were in very close contact, they rarely adopted each other's technology if it wasn't already similar to what they've been doing.
Agriculture probably initially expanded because farmers pressed north through the continent, not because hunter-gatherers adopted the practice on their own, Scandinavian scientists say.
If in this close contact scenario agriculture didn't spread, it's a huge stretch to expect very low level contact to make it happen.
All theories of emergence of agriculture I'm aware of pretend it happened just once, which is totally wrong.
Is these any even vaguely plausible theory explaining how different populations, in very different climates, with pretty much no contact with each other, didn't develop anything like agriculture for very long time, and then in happened multiple times nearly simultaneously?
Any explanation involving "selection effects" is wrong, since these populations were not in any kind of significant genetic contact with each other for a very long time before that happened (and such explanations for culture are pretty much always wrong as a rule - it's second coming of "scientific racism").
How does that reinforce Robin's model? It goes against it if anything. Imagine if humans, dolphins, bats, bears, and penguins nearly simultaneously developed language on separate continents. It would be a major unexplained WTF.
You can start here, but Wikipedia has pretty bad coverage of that.
Agriculture developed very far from regions most affected by glaciation, and in very diverse climates, so any climatic common cause is pretty dubious.
It seems rather easy to mess with the inputs T. Weather conditions or continental drifts could confine pre-agricultural humans to hunting essentially indefinitely
This is sort of amazing, but after a couple million years of hunting and gathering humans developed agriculture independently within a few thousand years in multiple locations (the count is at least 7, possibly more).
This really doesn't have a good explanation, it's too ridiculous to be a coincidence, and there's nothing remotely like a plausible common cause.
But in a field like AI prediction, where experts lack feed back for their pronouncements, we should expect them to perform poorly, and for biases to dominate their thinking.
And that's pretty much the key sentence.
There is little difference between experts and non-experts.
Except there's no such thing as AGI expert.
This is far more sensible judgement of Kurzweil's prediction than OP's.
Your judgment on all of these is ridiculously positive. Just about everything you claim as true or partly true seems to be mostly false to totally false to me.
Your argument depends on choosing what's "central" or "archetypal" example, and that's completely arbitrary, since this doesn't seem to mean "most common" or anything else objective.
It really falls apart on that.