Was kinda thinking about the same idea recently as well. Vanilla Pueblo had some cool 'refinery-esque' parts on either end with the triple-smokestacks and rotating bits that gave a ore-processing and industrial feel.. Posted below for reference:
I did see a refinery Model used in GC but think it was a Private Model, cause I never saw it any place else in the game. but I saw it over a year ago. and don't remember where I saw the darn thing but would like to see a full refinery model done, I think it will be really popular for sure with all these bases now doing refinery's