Rumor: Windows Phone 9 Will Be Built from Scratch
Microsoft is redesigning its mobile OS (again).
Microsoft took a fresh approach when designing Windows Phone 7. The operating system was a complete departure from Windows Mobile 6.5 and though Windows Phone 8 shares a lot of the same design elements as Windows 8 for desktop, it doesn't actually run the same apps as Windows Phone 7. Now it looks as though Microsoft is ready to redesign mobile once again.
According to Eldar Murtazin of Mobile Review, the next version of Windows Phones will be both a tablet and smartphone operating system. What's more, Murtazin says we'll see a whole new UI that will be different to Metro UI (though, he notes, Microsoft won't actually be able to admit mistake with Metro, as it's been pushing the interface so actively in advertising). He says the new version will be developed almost from scratch.
If you've been eying up one of the current Windows Phone 8 devices and are now panicking about it being out of date, you needn't worry. Murtazin notes that this OS doesn't yet exist and will likely only be completed in 2015.

http://news.cnet.com/8301-1035_3-57584784-94/windows-phone-jumps-to-third-place-in-smartphone-market/
Ironic that unless their approach to windows changes, the only place that Metro will continue to exist is on the desktop, where it was never a comfortable fit.
I VERY much hope for the latter, as I will NOT be getting another Windows phone without more free access to the file system and less of this syncing BS.
I am pretty sure Microsoft wants to achieve two things with all its devices, a unified interface so you can go from device to device without much change. They want an interface that will propel them into the leading smartphone OS.
Lets improve Metro on phones/tablets, but keep it on desktop!
Lets add a desktop to phones!
Lets improve desktop battery life!
How about a monthly subscription for OSs?
But it SUCKS for desktops....
Why is this concept so hard for MS to understand????????
Off course WP9 will be different than WP8.X... Otherwise it would be WP8.Y.
It will be touch based just like WP8, but a little bit different UI (everybody expect that from new OS version...). It will have some new versions and if this rumour is true, it will be the same as the version that is being used in RT type tablets... When phones are developing so fast, it is easy to see that it is more sensible to develop a windows version that can run also in phone and tablet. You can use same programs etc...
What does this mean regarding desktop win9, nobody know, but if I have to ques, it will be quite similar from UI perspective than WP9. A touch based "upgraded" metro UI. Let's call it Metro2 and you see the point...