There's already an "arp" section. Please just add a "chord" option under that same area with a basic triad shape. It would make it so much easier to play chords on my iphone using one note.
A secondary feature that would be nice, is vertical grid lines in the midi section based off the "grid size". That would make moving midi notes around a lot more intuitive.
Lastly, a "slice note" option to cut/duplicate the selected note based on the "grid size" would be extremely helpful as well.