I actually did some more testing and got some rather nonsensical results. Just setting R600_DEBUG=vs,ps makes the game run, even though all that should do is make the driver print debug info on the vertex and pixel shaders. Another similar option that works is R600_DEBUG=check_vm. Yet enabling some other options at the same time breaks it again.
I honestly have no idea what's causing this, or why the different debug options work. If you guys can test the issue with the relevant hardware and see if it can be worked around, that would be great. Older demos used to work without a hitch.
As a side note, I meant to report this back during DD13 already but forgot amidst all the other demos, sorry about that.