I'm curious how close the research community is to general AI

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://agi.mit.edu

https://agi.reddit.com

http://www.agi-society.org/

https://opencog.org/

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...

I highly recommend Markus Hutter's book: "Universal Artificial Intelligence: Sequential Decisions Based On Algorithmic Probability" (http://www.amazon.com/Universal-Artificial-Intelligence-Algo... )

Beware, you need some serious maths and a board to follow him. In the end the book is quite rewarding.

Now to AIXI: I don't belive that having a formula solves AI problem. Yes you can model it, but in real environment, I believe there are simpler models to try first. Remember: nature like simpliness first, complex when needed.