There is actually a lot of available space in downtown Dallas. Between city hall and I-30, from the convention center to the Farmers Market, there is a whole lot of nothing. The DMN had a story a couple weeks ago of a potential developer who wanted that section for a huge development that I want to say would accommodate 50,000 employees in several towers. If Dallas was really smart and forward thinking (its not) they would tear down the convention center and put that land to some real use with actual roi. Also, given that one of the dreams of everyone is to bury and deck I-30 through downtown, you could include the Cedars in the plan, just on the other side of 30. That's all on or near transit lines (including the future D2, and high speed rail terminal). Of course all of that would require a city with an actual vision