Nobody knows, because we don't know how to do it yet. There could be a "big breakthrough" tomorrow that more or less finishes it out, or it could take 100 years, or - worst case - Penrose turns out to be right and it's not possible at all.
Also, are there useful books, courses or papers that go into general AI research?
Of course there are. See:
https://www.amazon.com/Engineering-General-Intelligence-Part...
https://www.amazon.com/Engineering-General-Intelligence-Part...
https://www.amazon.com/Artificial-General-Intelligence-Cogni...
https://www.amazon.com/Universal-Artificial-Intelligence-Alg...
https://www.amazon.com/How-Create-Mind-Thought-Revealed/dp/0...
https://www.amazon.com/Intelligence-Understanding-Creation-I...
https://www.amazon.com/Society-Mind-Marvin-Minsky/dp/0671657...
https://www.amazon.com/Unified-Theories-Cognition-William-Le...
https://www.amazon.com/Master-Algorithm-Ultimate-Learning-Ma...
https://www.amazon.com/Singularity-Near-Humans-Transcend-Bio...
https://www.amazon.com/Emotion-Machine-Commonsense-Artificia...
https://www.amazon.com/Physical-Universe-Oxford-Cognitive-Ar...
See also, the work on various "Cognitive Architectures", including SOAR, ACT-R, CLARION, etc,
https://en.wikipedia.org/wiki/Cognitive_architecture
"Neuvoevolution"
https://en.wikipedia.org/wiki/Neuroevolution
and "Biologically Inspired Computing"
https://en.wikipedia.org/wiki/Biologically_inspired_computin...
Otherwise, HTM inventor Jeff Hawkins' book "On Intelligence" is one of the top 3 or so most fascinating books I've ever read. It doesn't cover HTM though, just how the brain works at a conceptual level, but in a way I haven't seen anyone else explain. Jeff clearly has an ability to see the forest through the trees in a way that is not too commonly found. This is one of the reasons I think HTM might be on to something, although it of course has to prove itself in real life too.
But we should remember for how long classic Neural Networks was NOT overly successful, and almost dismissed by a lot of people (including my university teacher who was rather skeptical about them, when I took an ML course on like 12 years ago and personally believed a lot in them). We had to "wait" for years and years until enough people were eventually throwing enough work on finding out how to make them really shine.
[1] https://numenta.org/
[2] https://numenta.com/neuroscience-research/research-publicati...
[3] https://www.youtube.com/user/OfficialNumenta
[4] https://www.amazon.com/Intelligence-Understanding-Creation-I...
Edit: Fixed book link.