Morkilus, thanks for the link to the GUI mod. From the looks of it, I still can't do what I had hoped. Dom2 let you load specific GUIs based on the nation you were playing. Seems the best we can do in Dom3 (still) is overwrite the image files for the single, universal GUI. Alas.
Also, that's awesome you've got Sylvania going in MP. I'd love to read the AAR from that game.
Great to hear you like those old mods!