ok maybe one year but by that time apps will be rewritten for 8.1. Stop doubting windows phone.
Have faith in WP.
True. But, Microsoft is Microsoft.
Let me clear that up by saying Apple's AppStore vs. Microsoft's Store. When the iPhone 5 came, most apps were only written for the resolution of the iPhone's before that one. So you saw two black lines. Within some months 80% of the apps were done. Done only by internal pressure from Apple.
However 80% isn't enough. So Apple said that if you didn't upgrade your app it will be removed. They didn't remove so many apps but it was just the pressure. A kind of pressure Apple's got away with. They did the same with iOS 7. Because apps needed to look and feel like iOS 7.
To the point: I don't see Microsoft doing that. At least not the Apple way. You say "one year" ... rumors say there's Windows 9 (Phone?) in Q2 2015 this means that all the apps are updates to Windows Phone 8.1 and we're possibly running Windows Phone 9. You see, there's no point. It's always running behind. The only good thing I see is the universal apps and shared code. I would push my developers to create Win/WP 9 apps and would leave 8.1 for themselves to develop for.
Faith in WP
Honestly I do have faith in WP. Simply because they make the hard- and software. The only other company doing that is Apple. And, even if we don't like Apple, we all know they are the industry standard. Microsoft got my eye because I fancy the start screen and the idea of bringing Desktop and Tabled together with Windows 8. And bringing Phone and Desktop together in Windows 9. So the future is bright, but not very sunny!