I don't intend to be rude to you, so please don't take any of this personally; unless you are of the people that implemented any of the 'popular' commercial UIs, in which case - "Thhhhhhhpurb" (attempted web-rasberry)
Why bother creating yet another look and feel when we all use and are experienced with what comes with our native operating systems?
Maybe because all of them are absolute junk. Windows is apalling, Mac is cretinous, Gnome & KDE make windows almost look good, Acorn is ridiculous. I just about tolerate Acorn because I'm so used (innured?) to it, but really guys, they're all just pathetic.
- Allow the use of native windows and widgets through an interface
that means you can write code that will work across most of the deployed platforms with the look and feel of those platforms.
This is just about doable. Portability in this is really difficult; I worked on a big project attacking it at ParcPlace. It shewed promise, but involved major work in FFI, callbacks, fixing bugs in the native widgets themselves. A mojor pain. During the work, we noticed that hardly any major applications actually used the native widgets anyway. M$ were particularly prone to this. There was a pretty damn good paper on this in the OOPSLA 95(?) proceedings.
- Develop a completely new and different user interface/experience
that will be wicked and weird and beautiful and, generally, make people's jaws drop.
I think that's what many of us are working on.
Perhaps both could be done, but it seems to me to be a waste of time to write code to make Squeak look like another operating system.
Web browsing presents a quite different UI to most OSs, and offers at least a chance that we can force open the door to something better. One of the things I particularly dislike about all the .NET BS is the transparent attempt by M$ to make the web look like windows. Yuck.