The latest blog post states that the EXTRO opcode was removed in order to create a market for data feeds. That strikes me as short-sighted, considering the advantages of permitting contracts to directly inspect each other's source code. That ability would open up a very wide set of behaviours; in particular, co-operation with a correctly formed 'stranger' becomes possible, even when neither contract contains knowledge of the other at the time of its creation, because their behaviour becomes known and deterministic. There's a lot of interest in this sort of thing on the rationality forum lesswrong.com; I was particularly excited to see extrospection in Ethereum because there are very few other contexts where the requirement of mutual knowledge of source code is provably satisfied. Would anyone else like to see EXTRO return?