I normally try to avoid this sort of fruitless fantasy exploration, but after using Windows 8 on the prototype Samsung tablet for the past month and a half, I've come to really appreciate some of the user experience improvements Microsoft has made to the Start screen. And I'd like to see some of them occur on Windows Phone going forward.
Central to these changes is the notion of navigation. On Windows Phone, there are two primary screens, the Start screen, or "home" screen, as some call it and the "all apps" screen, which is displayed by swiping to the right from the Start screen. Stacked side-by-side, these screens look like so:
Windows Phone 7.5 Start screen and all apps screen, side by side.
Each screen scrolls vertically, so you must move up and down to see more information. This becomes a bit ponderous over time as you add more tiles to the Start screen and more apps, generally, to the device. In each case, more stuff appears on each screen, making it more difficult to scroll through all the information and find what you're looking for.
Furthermore, this style of scrolling is far less common on Windows Phone than is horizontal scrolling, which is used by most of the system's integrated hubs, including Pictures, Music + Video, Office, and Games. For this reason, and because a left-to-right swiping motion requires less effort because of the width of the phone is shorter than its height, I recommend that Microsoft switch Windows Phone to this model. So instead of having to scroll up and down on the Start/all apps screens, you would scroll left to right and vice versa.
I'll take it a step further. There shouldn't be two screens, but just one, as with the Windows 8 Start screen. Every time you install an app, it is added to the Start screen, on the far right. You can remove (unpin) apps from this screen as you would in Windows 8, and to find them, you could utilize search (again, as per Windows 8).
A very rough example of how this could look is seen here:
The Windows Phone Start screen should evolve to work like that of Windows 8, and offer left-to-right scrolling.
As with Windows 8, this screen should include customizable groups so that the user can create a phone-based version of folders and organize things as they wish. And Microsoft should add the ability to easily contract and expand groups so that little-used apps could be hidden by default and be more easily swiped over. That could look something like this:
One idea for collapsable Start screen tile groups. (Shown here with three collapsed groups.)
This screen should orient itself automatically with the phone, so that if the user holds it horizontally (in landscape mode), the view switches to accommodate that and is thus not "sideways" as it is today.
From a customization standpoint, tiles in Windows Phone should work exactly as they do in Windows 8. The user should be able to toggle a tile between large (rectangular) and small (square, and half-sized) views, and in each case the large version of the tile should be used to display more app-specific information. And when editing a tile (which can be done as today, by tapping and holding, or as with the Windows 8 method, depending on which makes more sense on the phone), you should get the chance to uninstall it, as you do on Windows 8.
And obviously, app makers should be able to color their tiles as needed, and not have to conform to a limiting and bland color theme as in Windows Phone 7.x. The best apps will let you choose between the system color theme (for those that want it), the default app tile color, or a range of colors. And while we're talking themes, the color choices should be virtually infinite and should include a background image, not just a solid black or white color. Let users really make it their own.
Windows Phone 8 should also support a Windows 8-style Edge UI, both from a system-wide perspective (charms) and within apps. This could work much like it does in Windows 8 and doesn't bear much discussion.
Put simply, if you accept the fact that Windows 8 represents the latest thinking when it comes to a Metro-style UI, you should further accept that the best ideas from Windows 8 should be pushed into Windows Phone as well. In fact, where possible these user experience elements should be identical, to provide a similar or nearly identical experience where it makes sense. I feel strongly that people who see Windows 8 tablets and PCs in stores next year are going to be very excited by this system. And they're going to want it on their phones too.