Historically speaking, between average Android device and average Chromebook, latter is far easier to get mainline kernel + "normal" Linux distro running, e.g: 8 Chromebooks vs. only 1 Android device (and even that is a dev. board) in official Arch supported hardware list:
https://archlinuxarm.org/platforms
Alas, new Chromebooks are no more. "Successor" Googlebooks are all Android.
So Arch on ARM is basically limited to an SoC with at most 8GB of RAM? It looks like we are still very far from a mainstream ARM motherboard with a socketed CPU, upgradable RAM and support for discrete GPUs. Until then, I see no reason to move away from x86.