The Arcosanti 5000 Model was seen as the final iteration of the evolving planning of Arcosanti as the designated site for the World's First Prototype Arcology. The process began actually before Arcosanti when Cosanti in the 60s was still the official designated site for the world first prototype Arcology. However the story goes that Cosanti as it was being rapidly encroached by suburban development in Paradise Valley was no longer deemed by Soleri to be ideal site for the prototype. Thus a search began to locate a new site for the first Arcology development and in 1970 a cattle ranch near Cordes Junction/lakes in Mayer was selected as the default site for the prototype and has remained ever since.
Since then however there have been a series of plans for the development of the prototype and they have changed significantly over the years. Most recently in 2000, Soleri retweaked the previous 80s style development and added the Elongated Apses (Arcosanti 5000 Development) in the backside that would actually hold the bulk of the city. This building would rise to 25 stories in the desert and house over 2500 people and basically the entire length of the site from West to East. A second intermediate building called the West Crescent would house about 800 people and be the location of the major site hotel and convention center.
One of the major challenges to the Arcosanti 5000 development is that they are quite possibly some of the largest apses the world has seen and would involve considerable costs to build given the proposed angles of the apses and height that they will rise above the ground. Thus the budget for this project has been undefined but can be roughly estimated to be in the range of the multiple hundreds of millions of dollars. This as many visitors have pointed as quite ambitious and is quite a distance (at least an order of magnitude larger - 10x - in scope than the existing project) larger in terms of construction and logistical considerations than the scope of the existing 60 person 800,000 dollar a year project.
Between the here and now is the current project and the uber-ambitious Arcosanti 5000 lies an intermediate stage called Arcosanti Critical Mass which would house around 300-500 people and include the construction of several smaller building complexes including the Teilhard de Chardan Cloister, Pizza Piazza and the Energy Apron.
It is important to note that Arcosanti never has had a comprehensive master plan as a future development. Although some planning and design has been done they have not include a detailed financial and implementation plan. Similarly the organization developing the proposed projects mentioned above and also running the current site - Cosanti Foundation - is currently working on a Five Year Development Plan and Strategy for Arcosanti that might move the project more effectively towards the Critical Mass vision.