BEAM robotics, but with an AI based on this emergent type of decision-making, which I do believe is the path to C3PO.
Many years ago, I was impressed by a program outlined by Douglas Hofstadter called COPYCAT in his book Creative Concepts and Fluid Analogies. The goal of the program was to solve puzzles such as:
I change 'egf' to 'egw', can you do the same for 'ghi'?
The program was non-deterministic; successive runs would result in different answers. However, the program also measured the computation required to arrive at an answer, and the program could be written so as the 'effort' could bias the output.
I change 'aabc' to 'aabd', can you do the same for 'ijkk'?
1000 runs of the second program lead to something like:
There is no right answer, but some are more satisfactory than others. This was a very early version of what Watson does.
ijll: 612, ijkl: 198, jjkl: 121, hjkk: 47, jkkk: 9, etc...
It's fairly obvious that our own brains have competing processes, and that our decisions are the result of this competition. Check out what happens when you cut someone's corpus collosum. I imagine that some day, along this path, C3PO will appear to be of one mind, but will in fact be the emergent behavior of numerous processes running in parallel. He won't be programmed around a body of knowledge, but will absorb and create bodies of knowledge, and different ways to operate on them. Google's image processing software would be just one of hundreds, if not thousands of similarly complex processes that could be drawn upon. Of course, some processes would probably work to coordinate them all.
I give C3PO 15 years.