I compiled latest MESA GIT today and tried the SL viewer out once more. The
issue still exists! I have however at least found a way to test it, that
doesn't appear to crash my computer (have no prims in view and therefore
rendered, have a command ready to instantly kill the viewer process). I shall
see if I can test with different settings, in case it's a combination of
factors.

One thing I noticed additionally: I have Radeon DPM enabled, despite my Kernel
requiring a boot parameter for that as that's not yet default. When the issue
takes place, the fan on my video card also reach maximum RPM. Something clearly
floods the video card and GPU beyond what they can handle.