First time testing the Blinkenwall with the full setup (Blinkenwall + proper network cable + ODROID C1)!
The good news is, it works! After a few hours of fiddling, the ODROID C1 talked to the virtual 640x480 display and could show a small 192x144 window in it running OpenGL ES 2.0 (with the program I wrote in Rust), which was displayed properly on the Blinkenwall.
The bad news is, the performance of the ODROID C1 is abysmal. Where my notebook could render 60fps without breaking a sweat, I get maybe 0.5fps on the device. This means that my plan for the software implementation simply does not work that way.
Since I'm not willing to go back on that software idea, I'll probably move to another, more powerful SBC. Luckily, since we chose the Raspberry Pi form factor, there are some to choose from.
Next I'll try the up-board. It is the most powerful SBC in Raspberry Pi form factor that I know of and that I own. It's probably dwarfed by the Jetson TX1 in graphics performance, whose official carrier board also features the same 40pin-connector, but that one is far too expensive for this application and would also introduce some space issues in the server case.