So, I love the loop song parts feature. Especially that I can go to the part I want as the start, hold down the loop button and arrow to the last part in the loop. (Correction... this doesn't work exatcly as I thought.. so... maybe add a way to define the start AND end of the loop)
You could further enhance this by adding the ability to set the number of loops until loop-exit and continue. This would allow for more complex, yet shorter song structures.
One possible way to implement this might be:
1) In SongStep Mode with Rec enabled, set up the loop with start and end parts
2) Arrow to the first or last part in the loop
3) press ALT+[number pad entry] to set the number of loop iterations. An entry of 0 (default) will loop indefinitely
4) Release ALT key to set value.