The ability to create a drop down list of exercises in a program i.e. say a program consisted of:

A1 - Lower body single leg push - 4 x 6-8
A2 - Upper body pull - 4 x 6-8

B1 - - Lower body single leg pull - 4 x 6-8
B2 - upper body push - 4 x 6-8
B3 - core - 4 x 10-12

D1 - biceps - 2x10-12
D2 - triceps 2x10-12

The actual exercise variety would be populated with a list of exercises (say split squats, lunge and step up for single leg push). The sets and reps stay the same. All you need to do is hit the drop down and change up the exercises.

This would make altering programs SO, SO much easier. No need to search for new exercises. No need to un-superset and re-superset. No need to re-enter the sets/reps data.

This allows for an training system to be built up with quick individualisation for clients.