At this point it's clear there is a significant percentage of XU3 and XU4 users (myself included) that have tested all the Arch 4.9.x kernels so far (the 4.9.13-xyz series, and the new 4.9.20 revision) and it's getting stuck at "Starting kernel"
On the other hand I've been compiling the Hardkernel 4.9.x kernels for their Ubuntu distribution from the designated Git location and no problems there...