XGL enables us to think about some intriguing new, more 'human' concepts in earnest for the first time...
First, why not get rid of rectangular constraints and turn the desktop into a sphere of variable size?
This would open up totally new possibilities for re-designing the man-machine interface. How would you like switching to a virtual machine - or to the network - by zooming out of the sphere that is your desktop and turning to another sphere...?
Or zooming _into_ the sphere in order to browse the filesystem... Like cities becoming visible when you zoom in a satellite picture the structure of the filesystem could become visible. Zooming in onto your files shows previews that scale smoothly. When you zoom onto one file's preview till it fills the screen the application will already have started up and only the appearing toolbars will tell you that something has changed. The notion that one has to use applications in order to work should disappear as much as possible.
Or, if you zoom in another place, the system configuration or the network-settings could appear out of thin air. (Although I would prefer to get to the system settings by zooming through the 'desktop' into the 'core', perhaps with a nicely surreal effect of the water plugin.)
To make the 'desktop' more accessible for the average human being one should model it after the real world as much as possible. Make it a
globe and you'll never have to wonder where you left those quarantined files from the network - they're in Siberia! Want to store your artwork in the Louvre? - why, after all, not? Where do I find my Java tools? Well, naturally... Store your holiday snapshots exactly in the country where they were taken and/or in a representation of the cupboard you actually keep those photo albums! While it's not really important where you put it - the search tool (Beagle?) will find all you need instantly and take you there in a Google-Earth-style flight...
And why not explore whether Google Earth could somehow be integrated into this?
Your 'home'-directory would be where you actually are on the map of course - in your hometown. Your financial data is in the city bank, of course where you also find all apps and bookmarks that might be useful in the context.
The different 'layers' of the desktop that seem to be planned for KDE4 could work as different views on the globe, like night-view, infrared-view etc., each representing a workspace targeted at a different aim, a different user etc..
You could also use different planet topographies for different machines/virtual machines in the network, of course... How about a 'Mars' desktop for your server? Or for a different user? How about a whole Trekkie-universe for your company?
Handling of applications could also greatly benefit from XGL. I'd favour a variant of the concept seen in
Novell's SLED 10 'application browser' or the
xfce-appfinder with a twist. First you click a symbol and the application browser starts up and 3D-representations of program categories 'hover in the air' in front of the globe, a bit like in a media center or in the
Looking Glass java desktop. Select one categorie and it unfolds like a blossom, setting free 3D representations of the programs. Or type in a name of a category or a program that you're looking for and its symbol zooms towards you. Either start it or
zoom into it and see which files that application opened recently. The 'surface' of the file preview could feature an unobtrusive shiny mirror-effect which could reflect the environment where the file is stored. Like the reflection in a shop-window (or on a monitor screen...). Zoom into the file and you've opened it with the application.
It would even be more coherent desktop behaviour to substitute the whole 'klick to open' operating of the desktop with a 'zoom-in to open' approach everywhere (except for inside menus): Zoom into the application-launcher, zoom into the app-categories, zoom into the application, zoom into a recently opened document or into an empty one. One continuous, fluent motion to get where you want. Left mouse button to zoom in, right mouse-button to zoom out.
Windows won't have to be rectangular in KDE4, so why not make them bubbles of blue (?) liquid with previews and symbols floating inside them? Zoom into a bubble/window and still see the rest of the 'desktop', perhaps through the coloured liquid.
Important dialogues, like system notifications, could be designed to stick out by being the only sharp, rectangular objects in the desktop environment.
Why restrict concepts to 2D if XGL makes so many things possible? Programming a big milestone with KDE4, you might as well think big.
There's virtually no limit to what 3D acceleration can do for improving the desktop. (Wellll... It might mean overdoing it to expect Objective Camel projects trotting through a desert but you get the general idea....)
P.S. Yeah... I already know I'm crazy.