I believe the late 80's/early 90's plans would have involved removal of ballast to reduce weight, modifying the bogies to compensate for the lighter weight (they would out of gauge otherwise), regearing the motors/wheelsets for a higher top speed and ETH.
I think in the end the cost of doing it was going to be prohibitive so it was abandoned and they started looking at the class 48 which never got past the idea stage due to lack of demand.