If both boxes are transparent, then the problem is underspecified for agents whose action depends on what they see unless you add a rule to cover them. That doesn't mean that the parts of the problem which you have specified (namely, what happens to unconditional one-boxers and unconditional two-boxers) are invalid, just that you missed a case.
I have not seen any place to discuss Eliezer Yudkowsky's new paper, titled Timeless Decision Theory, so I decided to create a discussion post. (Have I missed an already existing post or discussion?)