They will have their reasons, why MIDI I/O isn´t made yet.
Maybe they fear some good questions when they reject this feature officialy?
Agreements with other developers to keep the ReWire compatibility with other DAW?
Imagine Reason would have MIDI I/O or just sends Midi to a DAW
Or maybe Reason´s got MIDI I/O and we´re all too dumb to use this and the Propellerheads are laughing at us to get motivation for the day.