Rep. Sandy Levin has introduced legislation for the creation of six regional primaries for choosing presidential nominees.
UPDATE: I received the following clarification from Rep. Levin’s office via email:

Congressman Levin’s primary bill is an interregional bill, not a regional primary bill. Where most regional plans hold primaries in one region of the country at one given time, Mr. Levin’s bill allows for every region of the country to be represented during each primary election date.
The “Interregional Presidential Primary and Caucus Act of 2007” would divide the country into six regions, and further divide each region into six sub-regions, consisting of one state or a group of smaller, contiguous states. There would be six primary dates, spaced out evenly between the second Tuesday in March and the second Tuesday in June. On each of these dates, one sub-region from each region would conduct its primary, ensuring that each region of the country is represented during every primary election. The order would be selected by lottery. States that hold their primaries first in one election cycle would be last in the next cycle, and then advance in order after that. This system guarantees that over a 24-year period, every state has the opportunity to hold its primary on the first possible date exactly once.
Essentially, each region of the country is represented during each primary election date in complete contrast to those proposed regional primary plans.
Feel free to check out this recent news article on Mr. Levin’s bill: http://www.house.gov/apps/list/hearing/mi12_levin/morenews/ar032707.html.