The Apple Cinema and Studio Display most certainly DID match the G4 (which is why they look so damn goofy and out-of-place beside a G5)!
The displays were silver, plastic, sporting curves and acrylic/clear accents. About the only thing that changed was going from a graphite Apple logo on back to more of a silver one, over time.
But those displays paired BEAUTIFULLY with the G4, even when the G4 underwent a few cosmetic changes (Sawtooth to Quicksilver to Mirror Door). They both had the same powdery silver, glossy look. The gentle curves and clear accents remained throughout all revisions.
As for the 6", I don't know. It's not a "gap" if there's something there (holes, a logo, power/USB, etc.).
I don't think they could just leave it blank aluminum, you're right.
As for simple, yeah probably. But again, in my drawings, I've put strokes around things and I'd assume Apple would engineer a tight, neat look. The drawings look cluttered because I'm trying to show that division/swing area where the "U" cradle meets the display proper.
As for "look at the previous Apple displays", two things:
1. I've probably "looked at them" more than you could ever imagine.
2. So what? Since when does the "previous version" of anything mean everything? Does the LCD iMac look anything remotely like the jellybean iMac? Does today's iBook look like the orange and blue "toilet seat" iBooks from 1999? The G5 deviated from the G4, the G4 PowerBook from the black, upside-down-logo PowerBooks too.
I doubt Apple would simply slap some aluminum on today's displays and call it "done". I'm sure any new displays will look pretty different from what we're used to!