Supposing it would be difficult to get the stock qnap firmware to do what I might want it to do for me, how hard would it be to hack SlackwareARM into the AnnapurnaLabs Alpine AL-212 SOC present in a Qnap TS-431 ?

Well there's a start with them committing to mainstream kernel: We are happy to announce that on February 8th 2016 we submitted to the mainline Linux kernel the initial support for Annapurna Labs Alpine v2 Platform-on-Chip based on the 64-bit ARMv8 architecture.

It's looking promising ... and the price is not that bad considering you're going to spend some 150 Euro on a bare 4 HDU bay case on top of which you need some sort of SBC and some sort of power supply.

The TS-431 uses the 32 bit Cortex A15 based cores tough ... and they say:

Now has anyone got one to investigate how it boots, where the kernel is and where the userland is ?

I'm seriously considering a hack on it to run SlackwareARM and maybe even run the original software in a container.

Looking further into the thing I noticed that there is an old TS-431 (with Freescale Cortex-A9) which is the one you can get for 250 Euro and a newer TS-431P with the Alpine (with Alpine AL-212 Cortex-A15) which is 300 Euro.

Now How's linux doing on the Freescale cortex-A9 mased SOCs ?