Various types of message processing, (precedents include JL Cooper MSB's, (which do basic note and octave transposition etc.) - of course the SeqV4 is a shining example of some extensive data processing possibilities)
For full Swiss Army knife utility - a further sophistication could be message-type conversion - i.e. note-to-CC, velocity-to-value etc. (might be a bit on the overboard side, but I've run into some situations - (esp. with gears that limit how and which messages can be interpreted), where it would be useful).
MIDI activity indication - could be just blinkenlights or ideally some sort of real-time message display as mentioned up-thread, for debugging and sanity checking
RTP MDI - (am not using this feature yet on SeqV4, but looking forward to having the ability to interface via wifi devices - could see it being very powerful for bringing in ctrlr editors for various synths etc).