Last Airbender co-creators Michael Dante DiMartino and Bryan Konietzko, along with voice director Andrea Romano and cast  Janet Varney (Korra), P.J. Byrne (Bolin), David Faustino (Mako), and Seychelle Gabriel (Asami) treated a crowd of enthusiastic San Diego Comic attendees to some secrets of what's to come in the future of Legend of Korra.

WARNING - PROBABLE SPOILERS

via Hollywood.com, co-creators Michael Dante DiMartino and Bryan Konietzko machine gunned some teaser facts about what's to come

• Team Avatar will travel to the Southern Water Tribe. 
• Concept art for the Southern Air Temple was also shown
• Book Two, called Spirits will take place six months after the events of book one
• It will explore and even visit the Spirit World with a look at how the "Avatar" lineage began
• Korra was previewed traveling through a storm to find a glowing iceberg very reminiscent to the iceberg Aang was trapped in.
• New costumes were also showcased
• Asami is now the head of her dad's Future Industries
• Tenzin's brother Bumi has a larger role
• His sister Kya is also a new regular
• Korra's expanded family will be introduced. The creators mentioned that Korra was inspired by MMA fighter Gina Carano, which explains her build. 

From elsewhere on the net (thanks to the original uploaders)