In urban combat the threat of an enemy targeting ammo in a rear turret bustle is very high but in open terrain the long range sensors and fire power of a tank offer the chance to minimise the risk to turret bustle mounted ammo, so something like the 31 round autoloader in the Black Eagle variation of the T-80 or the 31 round setup in the Burlak variant of the T-90 with the under floor 22 round autoloader suddenly become interesting.
I personally think having especially propellent and long rod penetrators in the rear turret bustle would make the crew compartment safer as these items are either most likely to ignite due to combat damage or benefit from a longer storage area respectively, would make the tank more effective with 53 ready to fire rounds and the ability to dump the propellent in case of a penetrating hit will make it safer...