If you can trigger more then 1 ability using a single keypress, that is against TOS (its a macro at that point). A dev stated this in discord not too long back. This is the simplest way to know something is against TOS or not.
I swapped my two action bars. I now have my ability bar with all macros going across, with my spells bar full of songs.
my macros:
/stopcast
/cast # (number on the spell bar)
Rebound all the keys on the ability bar to 1, 2, 3, 4, 5, ect... Now I can just hit 1, 2, 3, 4, 5, ect.. and interrupt my own songs. Works great.
Tying multiple songs together on one button is against TOS, macroed, hardware, mouse software, ect... This has been stated over and over. If you do, it's your access... your risk... they can detect it though...
Whats changing in the deep dive to help with APM (button presses)? No one knows yet.