The USDA is considering only two options:
1) fully deregulate GM alfalfa OR
2) conditionally deregulate it by placing certain rules and restrictions on growing GM alfalfa that would minimize or limit contamination of non-GM crops (including organic).
Far as I can tell from what available online, the only advantage of growing the GM alfalfa is that one can eliminate all non-GM plant life on the field by spraying the herbicide Roundup. According to Gurain-Sherman* using Roundup does not increase yields significantly, even over the short term. In the long run, weeds will become resistant to Roundup, either through naturally occurring mutations or through borrowing the Roundup Ready gene from GM crops. Herbicide resistance has already become a large problem in some locations (http://huerto-de-altamira.blogspot.com/2010/09/herbicide-resistant-pigweed-jobs-for.html)
*Gurain-Sherman,D. 2009. Failure to yield: evaluating the performance of genetically engineered crops. Cambridge (MA): Union of Concerned Scientists.