Allwinner SoCs are also absolutely unbrickable. This with or without an SD card. You can always get it to show up over USB by holding a device specific button at boot, and then you can get it to boot whatever you want.
The big advantage of the Allwinner chips (especially the mali based ones) is their very high degree of freedom. The GPU and VPU are the two bits which require work still, but progress is good. There is full u-boot source, there is full linux kernel source, and parts are making it upstream. All there is that is not free and that cannot be made free is the tiny bit of code in some microcontroller to make it act like a USB device during its special unbrickable boot mode.
Given that the RPi has a massively powerful DSP running the show on a 2MB large RTOS that is absolutely closed, the allwinner devices are _unbelievably_ free.