The new Apple campus is part of Robinson Ranch, which is the big undeveloped triangle of land between 45, Mopac North, and Parmer Lane. I did some searching yesterday and discovered that the area is already covered by a PUD agreement that allows high density, transit oriented development. The city signed the agreement with the Robinson family in 2004.
The Ranch is about 6050 acres, which is about 8-9 times the size of the Mueller development. Some of it is in a flood plain, but there is probably room for at least 7.5 Muellers. The city claims that Mueller will eventually have about 13,000 residents and 13,000 jobs. At the same level of development, Robinson could have about 100,000 jobs and 100,000 residents. That's similar to the number of jobs as Austin has downtown.
Capital Metro's Red Line runs right through the property and you can ride it from the Howard Station to Highland Mall in 20 minutes, and all the way downtown in 38 minutes. In the other direction, you can get from Howard to Lakeline in 14 minutes and it's about 30 minutes to the end of the line in Leander.
IMHO, the city needs to work with the Robinson family, the ranch owners, to come up with a long term plan for that area and start development, before it becomes a string of unconnected corporate campuses and a parade of slow-moving SUVs up and down Parmer.