My understanding is that Win 10 will automatically switch between a mouse and kbd interface to a tablet touch interface when needed.
Yeah, they're calling it "Continuum". But it seems like some of the useful features of the "metro" UI are missing from the Windows 10 preview. For example, in Windows 8 you can split the screen into two (or more, depending on your screen resolution) parts. You can have your regular desktop on one side and your metro Twitter app on the other side. It doesn't sound that impressive... Windows has always separated apps into Windows, right? But in the old Windows UI the apps could overlap each other which can actually be annoying. The split screen feature of Windows 8 means the two sides never interfere with each other. I can watch a video on one side while taking notes on the other side. The note taking app doesn't block the video app or vice versa. If I want the video to take up less space I can change the split ratio by sliding one bar rather than adjusting the sizes of two different windows separately. It works very well.
That doesn't seem to be the case in Windows 10 because the "metro" apps open in windows now, just like regular desktop apps. The split screen feature is missing as far as I can tell.
They have improved the regular desktop window "snap" feature (which was introduced in Windows 7) so that each window can be arranged in a quarter of the desktop space. It is very nice, but it's not as convenient as the Windows 8 split screen because each window has to be resized individually. If I resize one, the others don't adjust automatically. I find that annoying because I don't want the windows overlapping and I don't want to spend time manually adjusting the sizes of the windows.
So if you have one of those convertibles Win 10 will understand how it is configured and work accordingly. That feature was not ready for the recent alpha release but should be out soon.
I have a Surface Pro 3 (I'm writing this on it) and I'm curious about how well the "Continuum" feature will work. If I fold my keyboard back will it act like a tablet, or will it see that the keyboard is still attached and stay in "desktop mode"? I don't know... I just think that the touch friendly UI is useful even on a desktop, so I expect there to be times where Continuum gets it wrong. Time will tell.
The main change will be the banning of the metro/modern apps from the desktop, or whatever the full screen only apps were called.
Maybe I'm misunderstanding you, but I think it's actually the opposite. The metro apps aren't going to be banned from the desktop, instead they are going to act like normal windowed desktop apps. Which is not what I want. If I want to watch Netflix, I want it full screen. I don't want it in a window. I don't even want to have to take the extra step to maximize the window into full screen. It's for watching movies, so of course I want it full screen. Of course I don't want there to be title bars or task bars on the screen. I only want to see the movie. That is why I like metro apps for certain "media consumption" roles.
But from what I have seen in Windows 10, the metro apps always open in a window rather than full screen. And even after maximizing them they still have title bars and the taskbar on the screen. It annoys me. I'm hoping it's just because it's an early preview, but since it is the opposite of how they already worked in Windows 8, it seems like this is by design.
Playing with those on my kids laptops is what soured me on Win 8.
The way I see it, there is a purpose for the full screen metro apps (mostly for entertainment and media consumption), and a purpose for traditional desktop apps (content creation). If one suits your needs more than the other, then the option is there to use it. No one is saying you have to use the metro version of Internet Explorer, for example. If you prefer the desktop version then it's still there.
Like I said in another post, I use Windows 8 for work. I spend all day developing websites using Photoshop and Dreamweaver, FTPing, and working with MySQL databases. My favorite apps are pinned to the task bar, so I rarely see the Start screen. The only metro app I use at work is one for accessing internet radio stations. So I don't see the traditional desktop UI going away any time soon, but I do appreciate the metro UI too.