User generated mods would be amazing. I've played Tribes since Starsiege: Tribes in 1999, and I can definitely say that T:A is fantastic. It would be glorious if they had mods, though. Despite claims that the updates are slowing down, the community is certainly still alive and kickin'. I don't know if anyone remembers this, but back in the T1 days, there used to be a mod called Annihilation. It was made by a guy named Plasmatic. The dude is still playing T:A, I saw him online a couple of times!
At the end of the day, mods or no mods, T:A is so wonderful to play. There is no other game that gives me the satisfaction I derive from the mid-air disc, or from simply having a jetpack.