There are many challenges for AI, but IMO the biggest is to reduce the energy
cost. IIRC (and I'm happy to be corrected!) about 8% of the world's current
total energy production is used by AI applications.
Human brains are about 100,000 more energy efficient than silicon-based
processing, so it might be that huge arrays of "mini-brains" are the way
forward.
Here's a very recent article showing a lovely little mini-brain (I imagine)
bopping to a tune only it can hear.
https://www.quantamagazine.org/mini-brains-go-modular-20170809/