Several areas in data remanence can benefit from more investigation. After the adequacy of overwrites to ensure purging is determined, the use of disk exercisers for the purging of magnetic disks should be researched. Because of the increasing use of magneto-optical disks, research should be initiated on methods to purge this media also.
A good primer on magnetic coatings used for disks and tapes is Particulate Magnetic Recording: A Review, by Michael P. Sharrock.  For a discourse on future storage trends, see Data Storage in 2000-Trends in Data Storage Technologies, by Mark H. Kryder.  The IEEE Transactions on Magnetics provides a wealth of information on the field of magnetics1 with entire sections devoted to engineering-level discussions related to magnetic remanence in AIS storage media.
Announcements concerning cavity degaussers should be forthcoming. See the Degausser Products List for these announcements and for announcements about decisions concerning magnetic media degaussing.
DoD policy, procedures, and guidance need continual refinement to keep pace with the evolving storage technologies. Although there is no focal point responsible for ensuring erasure standards are current, various agencies have sponsored research that has ensured our erasure standards provide an adequate degree of security. This has caused duplication of effort at times, but it has also provided additional validation of earlier work. However, a focal point would ensure research is duplicated only when necessary. As storage technology advances and clear and purge procedures are developed and refined, this guideline will be periodically updated to reflect the changes. DoD 5200.28-M should be updated also.