I have the same bike (no problems) but I am interested. I'm looking at the diagrams & see some interesting things: the fuel pump relay gets power from the key through the bar kill switch. The relay feeds power to both injectors and the fuel pump, but it also feeds the O2 sensor and the tank breather valve. A short in any of those would take out F6 (10A). kinda groping, but a guy could disconnect the O2 & tank valve just to see if it changes things. I have to think that if the pump relay is not chattering then the problem is either the Motronic or one it's inputs. If the relay is chattering it could still be the Mo because it supplies the ground path for the pump relay. I don't remember if you said the Motronic's plug has been cleaned yet but it should be, also switching out relays is a good tool to isolate problems and the Motronic relay is the same as I recall.
another interesting part... the Motronic triggers both injectors to fire off pin 20, through a (Yellow/gray wire) which also connects to pin 10 in the diagnostic plug. it fires both at the same time
I don't see how the Hall senser could make the injectors fire if the motor isn't turning, but a guy could try disconnecting that one to see
long & short of it.... I would bet first on a bad relay or a cruddy contact... possibly the key