If the current Step structure changes, how can medical schools that make promotion decisions (from MS2 to MS3) continue to make these decisions?

Changes in the structure of USMLE exams may have little or no impact on schools using USMLE performance for other purposes. However, the NBME recognizes that medical schools use the results of USMLE examinations for the assessment of both individual students and of the schools’ educational programs. In implementing changes to the USMLE exam sequence, the NBME will be attentive to other assessment needs and the secondary uses of USMLE.

Source: http://usmleworldwide.com/blog/?p=141