I'd really like a sidechain on the delay effect to add in a modulation or distortion (or other) effect pedal on the delay tails. This would allow a nice build up of more analog sounding delay effects as well as awesome pad like sounds.
Then I'd like a multitap delay to set up more complex delay effects, this would offer at least two extra delay times per channel (and possibly a randomized delay option).
Finally I'd like a ducking option against the input signal.