It's funny that the Apollo project should be mentioned, since my hostname has been Parnassus for most of this year.
Though I've not touched it in almost a month, I've been working on an model - call it a vision, if that's your cliché - for GNOME. I've been putting recommendations on my website. Some people have been reading them (according to server logs), but none have replied to any that haven't been announced. (Which is probably good, given the flux. Still, it's lonely.) Those are not the model documents, but they bear at least one resemblance: they're boring.
Boring. That's what most of the recommendations and the big picture will be. Why? Because we like you! . . . No, wait, that's the mouseketeer song. Well, maybe that's appropriate because it is the mouse that binds us. The keyboard, pointer, and smaller-than-a-cubicle-wall rectangular screen will be the primary interface to the general purpose computer for most people for many years.
Unless GNOME starts making hardware, it had better be boring - a WIMP interface - like the Star, the Lisa, the Mac, OS/2, Windows, and all the rest. Without manufacturing wetware, you can't, with fiscal responsibility, consider Hollywood movie interfaces for which you need all your body parts in working order.
Boring doesn't mean there isn't room for improvement beyond existing interfaces, but neither GNOME nor any other X-based UI has caught up to MacOS or OS/2. There may be niches of excellence, but the X environments are inhospitable. Most of the recommendations I've put on my site are meant to clear the air so we can get a look at the landscape. Poor window management, drag-and-drop, and clipboard handling are a thick smog.
When those are out of the way, the X environments will probably be equal to Windows. At least then the foremost differences will be the quality of the applications. Assuming GNOME's HIG is cleaned up and followed, GNOME should easily surpass Windows. This could happen as early as the 3.x series.
What remains after that requires more code and much more persuasion. Since today's usability gurus can't move Microsoft or Apple to implement something as basic as user object persistence, I should have little hope.