Tribes: Ascend, and develop the franchise into a full-fledged MMO. Things have changed since then -- Hi-Rez's COO Todd Harris says, "right now our Tribes dev team is working only on Ascend."
Speaking to PC PowerPlay, Harris described Ascend as borrowing heavily from the earlier, fondly remembers Tribes games. Focusing solely on an action game means Hi-Rez could make sure to "get the movement and physics and combat feeling right." Some settings and weapons from the first game will return, but there will be new content, new weapons, and frequent releases of cosmetic items ("much the way League of Legends does in the MOBA genre," says Harris).
Both the MMO and single-player content are possibilities for the future, Harris adds, but Tribes: Ascend is the focus for now.