You know... I just had a thought... Do you have to render the entire thing? If you were to render a 1" x 1" section of it and place copies of that next to itself on the build plate, you could go to any size that made sense. Or if you wanted to keep it all in source form, with the new OpenScad you could render the 'child()' object and then use that in a multiple for() loops to make it as big as you wanted. The way OpenScad handles children is it only calculates and renders it once, and then it gets used again and again by the parent. It would probably dramatically cut down on the processing time. Maybe you could go crazy and use a very high $fn number and not bog things down.

You would just have to make sure the pattern replicated faithfully in all directions.