Play Mode: a choice to use the middle footswitch for repeat (nice to have but rarely used) or to punch-in the second delay (essential for reggae, dub, dubstep, dance, etc). So you could be playing with just the first delay on a short setting, then punch-in a long second delay to affect only the notes played while the footswitch is held down. This would echo away into the universe while you continued playing rhythm with the first short delay intact.
Please. It would add a lot of functionality to the second delay that is often unused.