1) Would the cost and trouble be less for a pair of PCB-mounted RJ45 jacks compared to the pair of pigtails?
This could really be argued both ways... I think by having it use pigtails it makes it more flexible. Its also harder to use RJ45 jacks and put it into a PVC pipe. You would have to drill a bigger hole in the end cap or put a new end on the cat5 cable. Also If you only need to go a few feet you could get away with just cutting a cat5 cable in half and soldering that in. You could also solder a male on one side and a female on the other or the other way around. It just all depends on where the user is looking to put this.
2) Would your processor be able to provide (4) DMX universes with the 4 pairs of wires? Downstream you could use a (de)combiner to separate out the 4 pairs. (this approach would mean no pass-through power, but most DMX devices wouldn't know how to handle it anyway...)
The PIC I am using only supports 2 serial ports (PixelNet IN, DMX OUT). So to add any more outputs it would take a big re-design (more chips and software). Sorry its not going to be possible right now.
The power on the output side (on the right) was meant to go with the pixelnet data that is also passed to that side of the board so that you could still run a SSC after.
Thank you for the suggestions keep them coming... but for now I think the HW side is good.