Data centers today are building to incredible density based on a guesstimate of what will be needed in the future. Some of this may be a huge waste as new liquid cooled processors begin to hit the market. The cooling capacity to build an extremely high density data center may not even be needed in a couple short years. Companies such as IBM have already started deploying the technology. Rear Door Heat Exchangers from companies like Coolcentric (Vette) and others can add the cooling directly to the cabinets required.
The answer, don’t overbuild. There is no reason to oversize air “just in case” when other solutions are either readily available or soon to be available that will allow you to build high density areas, not high density data centers covering the entire floor space. Rear door heat exchangers can be added where the capacity is needed.
In short, you need to pay attention to new technologies when planning for the future.