After the excellent Monaco Grand Prix this year (2011) I started doing a bit of research. The route (zoomable satellite image)
could be rotated just a bit in some places to fits a NSEW grid reasonably well.
Using the textures from Golden Lap, it would be a feasible track to build. With scenery and slopes, because it covers a very narrow area in most places. Could be built like the Gran Turismo and Gran Turismo 2 tracks, just a narrow corridor with basic scenery.
My earlier suggestions to make 45° and 22.5° bits line up better would help any race track mods. The geometry of Monaco's tunnel and main straight are especially in need of this, so we can use several smaller kinks instead of just one or two. Would also let us follow the shape of the complicated chicanes and angular corners better.
(EDIT) I won't make this, btw, I'm just giving the idea to the community.