Yes, cycle-accurate is very expensive because it prevents optimization. But as described they say they're doing an AOT version of cycle-accurate anyway?

In some ways this is similar to the concurrent-systems problems that memory barriers are a tool to address. Your emulator will come in two halves, a CPU side and a gfx/sfx side, as well as control inputs, and the "intermediate" approach is when you're just trying to preserve the sequence of load/stores between the two with an accuracy relative to frame timing. Maintaining ultra precise timing within a frame imposes more detailed coordination requirements on both sides of the emulation.