There haven't been many FMPA-only new features in the past couple releases, so here's an idea that I've long wished for:
The ability to define a "pause on calc", similar to pause on error, where you get to define any calc in the world and the debugger checks after each script step to see if that condition is true (and if so, then pause the debugger).
To me, this would really speed up debugging in those questions of "how did the variable become that", "how did I end up on this layout", etc. Stepping through complex scripts and sub-scripts and sub-sub-sub-scripts can be time-consuming and frustrating. "Pause on calc" would just get us right to the heart of the matter.