i've just found out about this project from the "OPU Winter Reunion" newsletter, and this is truly a great news that someone took onto making OP in 3d.
i guess it's way too early to seriously comment the graphic part (as you said it's meant to change anyway), but are you going to use dynamic shadows and bump-mapping? haven't seen how it's done in that engine you're using but usually it's not that hard to make, using the right textures.
and, about the textures, i have a copy of FilterForge software (professional edition) that's meant specially for textures generation. i've got it not long ago and still in a process of learning, but there's a lot of pre-made presets for textures that i can use to generate the new ones. so where i'm leading it, if someone is going to make the graphics part, send me a message and we can see what could be worked out
more about filterforge and examples
are here