While theoretically attractive, this is probably not feasible. Firstly, there is the "herding cats" aspect of getting graduate departments to agree - medical residency programs are much more regulated by and accountable to their accrediting boards. Second is the highly varied constituent departments. For example, a student interested in neural engineering may end up applying to a biomedical engineering program, an electrical engineering program, and a neuroscience program. Getting all of these into the same match system would be difficult, as their applicants would otherwise not likely overlap. (Residencies, in contrast, are much more homogeneous in nature - you pick surgery, or pediatrics, but rarely both). Finally, this would ultimately be a disservice to the student. In contrast to residencies, alot of a student's evaluation of a program is made after admission, when in-depth consideration of and interviews with individual PIs are done.