In this context it is important to understand AIRBUS' approach with regard to certifying operation with low fuel levels.
They say that according to flight planning requirements you arrive your destination with minimum diversion fuel, go around, divert to alternate and arrive there with only final reserve fuel remaing, i.e. an endurance of 30 minutes which translates into roughly 1.0 - 1.2 tons on the A319/A320.
A go-around at the alternate is not taken into account from a fuel-management point-of-view although 1000 kg FOB would enable you to go around, fly a short radar vectored pattern and land with at least 400 kg remaining.
AIRBUS says Final Reserve Fuel is only for Holding and now take your seats:
If you go around or otherwise exceed +10° of Pitch you might flame out any one or even both engines.
As mentioned above, as going around at the alternate is not figurde into minimum fuel requirements, there's nothing in the books with regard to this, remember 'it's the best aeroplane in the world'.
The only small hint is in System Limitations / Fuel, as the min. FOB for takeoff is 1.500 kg or just the warning Threshold for L+R Wing Tk Lo Lvl. Nice try, uh ??!
Back on Topic:
It's a certification requirement that for Take-Off and Landing both engines may NOT be feeded from the same tank as it might be the case with Fuel X-Feed open depending on the outlet pressure of the fuel pumps. That's in my opinion the reason for NOT opening X-Feed with both wing tanks low level.
BRGDS, Max