Right now output sockets for custom nodes are ordered based on when they were created. We can reorder them by copy pasting them in the order we want them to appear, however this is not obvious to the users. I think it would be more intuitive to have the output sockets based on top-to-bottom Z sort order of the output nodes.
edit 12/13: Coming back to this, I realize that it should be Y not Z location. Anyway I’m sure you guys understood what I meant