Open problems are clearly defined problems1 that have not been solved. In older fields, such as Mathematics, the list is rather intimidating. Rationality, on the other, seems to have no list.
While we have all of us here together to crunch on problems, let's shoot higher than trying to think of solutions and then finding problems that match the solution. What things are unsolved questions? Is it reasonable to assume those questions have concrete, absolute answers?
The catch is that these problems cannot be inherently fuzzy problems. "How do I become less wrong?" is not a problem that can be clearly defined. As such, it does not have a concrete, absolute answer. Does Rationality have a set of problems that can be clearly defined? If not, how do we work toward getting our problems clearly defined?
See also: Open problems at LW:Wiki
1: "Clearly defined" essentially means a formal, unambiguous definition. "Solving" such a problem would constitute a formal proof.
Using simple languages is the conventional approach. However, simple languages typically result in more complex programs. The game of life is very simple - yet try writing a program in it. If you are trying to minimise the size of an emulator of other languages, then highly simple languages don't seem to fit the bill.
Why would one want a decent formulation of Occam's razor? To help solve the problem of the priors.
I agree. We seem to have the same goal, so my first advice stands, not my second.
I am currently trying to develop a language that is both simple and expressive, and making some progress. The overall design is finished, and I am now down to what instructions it should have. It is a general bi-graph, but with a sequential program structure, and no separation of program and data.
It is somewhat different from what you want, as I also need something that have measurable use of time and memory, and is provable able to run fast.