I would totally be down for this except for the fact I seldom look at my G19's LCD screen as much as my monitor, so my 2d radar is positioned right on top of my cross-hairs; in some games, several pixels below.
It can still be nice though because I don't use the window for the 2d Radar, and sometimes depending on the colors on the screen some dots may be hard to spot. So if you want to take a good look behind you, looking down at a 2d radar with good contrast isn't such a terrible idea. :]
Won't make or break the experience though, I think the biggest thing I like is setting key-binds to G-keys anyways.