As I recall, most core T1 devs had all but left Dynamix early into the development of T2, once the foundational elements of the Torque engine were up and running. After that, it was left to others to actually design the game. People like Dave Georgeson had far more impact on the actual creative side of the end product of "Tribes 2" than Frohnmayer or Tunnel did.
As for a successor game ... (sad as it is to say) Tribes is dead, the IP has way too much baggage attached to it, leaving any game associated to "Tribes" with a serious hill to climb to restore itself and win back its glory days.
Plus ... there is the matter of a certain publisher owning the License adding even more baggage ... but that might actually be a good thing if it forced someone to abandon the appeal to nostalgia and just invent an entirely new IP anyways.