I don't have anything about a purely humano-centric Traveller universe, but if I were to announce such* to a new group of hopeful, eager players, the looks of undisguised disappointment would cause me to cower under the table until they decided to leave. Therefore I like to leave the door open to the possibility of a small numberNot being sarcastic or anything, but it is possible that they might prefer playing a Star Wars type game if they are so into being an alien species?
Now I'm wondering, and I haven't looked at the CT books for a few months (but I'm going to start some games again I hope so I need to), but isn't an alien-free galaxy the implied default along with no central government in the Classic Traveller setting? That later editions aliened-it up?
If I do have the party encounter sentient life in future games (I have them knocking around the edges of the frontier), it's more likely to be of the kind the usual Cosmic talking heads talk about these days on the science channels. Life that is not usually humanoid, if fairly unrecognizable. More like The Horta or the Xenomorph or a gas balloon (things players probably would not want to run) than Wookie or Twi'lek. The "ancient species seeded the universe with humanoid DNA" chestnut is something I would rather avoid.
I always thought the 2300 aliens were superbly alien-alien.