Nokia is working on the upcoming Symbian OS. Symbian Carla will be released in late 2012 or early 2013 followed by Symbian Donna about a year later.
Symbian Carla is intended for smartphones with a 1GHz processor or higher and is set to introduce a new version of the Nokia browser, version 8. There’s also new widgets, more NFC capabilities and support for Dolby Surround sound. Unfortunately due to the minimum processor requirement, it means that all the Symbian^3 and Symbian Anna handsets (N8, C6-01, C7, E7, E6, X7-00) are not going to get this update.
As for Symbian Donna we only know that it is made for smartphones with dual-core processors. Symbian smartphones in the year 2013/2014 would definitely run on dual-core processor(maybe more cores) although we are already seeing quad-core processors right now.
Nokia plans to abandon Symbian in 2016 so there are at least 4 years for Symbian to live.[Source]– IntoMobile