The game wasn't financially successful, but the developers nonetheless learned a lot of valuable lessons which led to Tribes: Ascend. While Tribes was well-received, it's something of a niche game due to its high player-skill requirements.
According to a blurb posted last night on the Hi-Rez forums, Global Agenda 2 is officially in the works and it will feature a focus on PvP. "We plan to add new maps, game modes, class weapons, and build it all on our newest platform," Hi-Rez says. The company hasn't officially named the title as of yet, but it expects to start beta testing by the middle of 2013.
[Thanks to Zeds for the tip!]