I've been a long time fan of Windows and love what they are doing with Windows 8 and Windows Phone 8. However, I think it is possible that BB10 could push WP8 into 4th place which could effectively kill the platform. Not that I think it will happen. MS has deep pockets and aren't going anywhere but it is clear MS is slow to "get it" sometimes.
Top 10 reason BB10 could be a major threat to WP8
1) Multitasking, finally done right. WP8 tries but the solution is half baked.
2) Notifications are best in class. I haven't seen a UI yet that is better than blackberry in this department. If you don't believe me check out the leaked concepts on french toast and cinnamon toast.
Blackberry 10 Cinnamon Toast and French Toast UI slides leaked | Ubergizmo
3) Windows has an integration problem. Everything has the Metro coat of paint, but that doesn't mean everything plays nice together. Wouldn't it be nice to start videos on an Xbox, pickup on a laptop/tablet, and finish on your phone? What about pickup a game a continue playing? Why do all the windows devices seem to have problems with each other?
4) Microsoft refuses to let go of IE even though it is generally slower than webkit based browsers.
5) Microsoft refuses to leverage its strongest brand, Xbox. WP8 should have the best mobile gaming platform period. Why hasn't it happened?
6) Microsoft wants to be too much like Apple in the mobile arena. Open the wall garden up.
7) UI elements are often too dumb downed. Simple is good, but often times being to minimalistic removes options that should be readily available and in plain sight.
8) Multimedia syncing isn't that great without the Zune App.
9) Where are the apps? Microsoft has promised a ton of top apps from other platforms but where are they and what are they doing to get more?
10) Microsoft and Google aren't friends = no good native google apps
11) RIM still has a huge following.