> many AArch64 processors [...] lack big endian mode while the cheap RasPi 2
> and 3 models retain compatibility to the ARMeb big endian support.

All AArch64 processors support BE8 mode, which means big-endian data encoding and little-endian instruction encoding, and all AArch64 processors lack BE32 mode, which means they lack big-endian instruction encoding. The BCM2837 with its Cortex-A53 cores is no exception to that. More info and references:

https://morph.zone/modules/newbb_plus/viewtopic.php?forum=3&topic_id=7675&start=522