Every time you hit IWT your character recomputes and executes a path to the target. If the target is mobile in any way your going to be running as you an see if most melee "maypole dance" videos. This pathing also queues with latency, so running off into the distance, the obvious attacking the next mob targeted moments after you have pressed IWT, and most annoying I think looting corpses in combat.

Anyways you don't want to chain your IWT with every DPS spell your melee guy casts more than you have to to get the character at the hitbox. On movement fights and in PvP obviously people need to keep up with the target and they find the run around disorientating and funny. Looking at the videos of people doing it its hard not to see why it should be removed from the game as used. It just looks like an exploit on its face.

You for sure don't want to automate the IWT key and your DPS key to be both sent via the multiplexer. You could code the multiplexer to rotate two keys IWT on the first press, DPS on the second, IWT on the third, DPS on the fourth, etc (likely a IWT,DPS four times, IWT, DPS four times) off one physically pressed key.

Having DPS keys, a manual "all melee dps IWT", then in the multiplexer "IWT/DPSxn" rotation asym key, maybe a "IWT/DPS" tight loop asym key if needed for some reason.