Microsoft Build their annual developer conference (think google I/0 or WWDC) has been announced for April 2-4 next year.
http://www.buildwindows.com/The Verge and Windows Phone Central both had details for the Windows Phone 8.1 update slated to release around the same time as Build.
http://www.theverge.com/2013/12/16/5215484/windows-phone-8-1-features-notification-center-cortana-Cortana voice program to rival siri and Google Now
-notification Center
-separate voice and volume settings
-Bing Smart search like Windows 8 have
-Xbox Music and Video are being separated from the OS to ensure faster updates
-VPN for enterprise
-deeper integration for social services for the people hub
Two new Nokia devices codenamed Moneypenny and Goldfinger are in the works as well. The update sounds like a big one and should bring WP to Parity with ios and Android. At this point all three are mostly about refinement and are barley doing anything new.