I doubt you will see Air Tran go into LAS
First, Southwest (enough said on that subject)
Second, It is a hub for America West
Finally, The 717 fleet Air Tran is acquiring has a range of about 1700 NM and that puts most of the west coast out of range of Atlanta.
I think there are plenty of markets for Air Tran to focus on in the east and midwest. I would not expect any growth in the West or the Northwest.
In order to really make the west work Air Tran would need a midwest hub to reach either coast with the 717. And as they have no other type in their fleet and I do not believe any intention of ordering another fleet type that would mean they wouldn't be poised for such growth. Sorry to really the bad news. They do tend to dilute and bring down the fares in markets they serve... But hey you have Southwest out there to do the same thing and heck they do a better job!