Step-by-step execution of BGE mainloop for debugging? I'm wondering whether it is possible to run the game engine in a "cycle
- by - cycle" fashion. 

I.e. a sort of debugging mode where one could
associate the mainloop cycles to keyboard events (for example) rather
than a time interval.
A simple way to go would be enable the console and to add a Always actuator somewhere with pulse mode enabled, linked to a Python controller using the following "script" :

input("Next step ")


Then at each step the python script will be blocking the whole execution until you press enter for the input to return.