The worst scenario is surely if it happens in the climb and you can't return to your POD (for whatever reason). Passing FL150, you must put the X-Feed on and start timing for 30 mins when you get above FL300 after which time you can put the X-Feed off again. But what is the imbalance when you put the X-Feed OFF after 30 mins. FL150 to FL300 - 500kgs? 30 mins in climb and then cruise at, say, FL350 - 1.5T? So by the time the fuel is aerated you are 2T OOB. In itself, that's ok, but you cannot restore the balance, so have you enough in the lower fuel wing to complete the flight? It could be embarrassing. It's probably best to land somewhere you can get it fixed. You can only dispatch with 1 pump inop.
Food for thought.
I haven't yet thought about the implication of the new A320 fuel system where the CTR TK fuel is transferred by jet pumps!