A big chunk of NX4 Xilinx code (with precompiled binaries and python code to talk to the tile over UART) just posted: https://github.com/raplin/OpenNX4
Currently the code supports taking to a host over UART (e.g. loading images onto the NX4) and python code is provided to make it do stuff.
It's currently in an 'advanced user' state, there remains one vital thing to figure out on the NX4; how to get the row scanning working (i.e. how to get the CPLD on the LED driver board to play ball).
Once we get that sorted out we're fairly far towards a working, daisy-chainable video tile, controllable by a variety of hosts (Ardunio, embedded linux, etc) using a variety of protocols and doing a variety of 'intelligent display' tricks.
We should be able to end up with something you can flash onto a tile in a minute or two with a cheap JTAG adapter, and accepts further firmware updates over the wire
The blocker right now is the CPLD (not) doing row scan...
Here's a really, really bad photo where I'm moving the camera so you can see the scanned image (original inset). The tile itself seems high quality; you can get excellent intensity gradients on it, and the 1/6 scan rate w/12-bit CC drivers is a luxury.