[hyp0]

You're being a bit parochial, specificially anthropocentric. Why a human brain? If you consider it's possible that other intelligences exist in the universe, they probably won't have human brains... Or, consider other animals on earth: given several million years and the right conditions, do you consider it possible that intelligence (at our level) could evolve again - and I don't just mean apes, dolphins and elephants. Especially fascinating in this connection are parrots, crows and other corvids, which are obviously quite intelligent, but have a completely different neuroanatomy of the higher centers from mammals.

Are really we so special? Apart from being first (that we know of)? The history of science is a history of anthropocentrism iconoclasm!

Of course, copying what we know works seems like a reasonable starting point.

Secondly, who said it has to be done within a few decades? If it is done within centuries or millennia, it is still done. "Infeasible" would mean it can't be done, ever.

Personally, I tend towards 50 years off... as it has been for a long time (and probably will continue to be) <- this is a joke. I'm saying it's a looong way off.