We can currently set the tempo of the Arp as a modulation destination, but we cannot choose the subdivision (1/4, 1/4T, 1/8th, etc) as a destination.
There are plenty of musical applications for doing such a thing so I think it would be worth it for you guys to attempt this.
Also, we should be able to set the amplitude/volume as a destination as well. Why can't we do this already for tremolo effects etc? Unless I'm missing something, this could be done by holding one of the three assign buttons and moving the volume knob or pressing the Amp Mod button...