I too would be shocked if all the proposed towers were to get built. I think that this one stands a good chance to make it. From what I know about CBL, they have a pretty good track record of getting their projects done in Dallas and Austin. Anyway, I hope this one makes it as I think it is my favorite design of all the proposed towers.
The projects that I have the most doubts about are the ~700 footers. It seems like 5th & Congress has been stretching on forever with no action in the last couple years other than renderings coming out. I'm not sure about 200 Congress, I don't know the history of Benchmark Development to know what to expect from them.
As far as the projects that I think have very good chances of making it(excluding the ones already under construction). I think the Spring will having recieved financing for construction. Novare's project at the post office site, although it will probably be a couple years before it starts. Then the projects with hotel chains involved which include the W and Hotel Van Zandt.