I don't believe any of this is confidental, but I've spoken with a student who's a liason to the NBME. This was after I read the thread Law2Doc was referring and the original post was basically legit.
The gist? The plan is to combine Step 1 and Step 2 into one monster test you take at around the timetable of Step 2 now. The test would encompass everything you learned in medical school, however it would continue the "clinically relevant" trend the Steps have been trying to take.
The suggestions of why this change has been made are basically to allow schools to integrate more clinically relevent stuff earlier in med school and cut out some early "never see it again except on Step 1" baloney you see in classes like Biochem. The suggestion was made that first year anatomy would include a lot more physical diagnosis and imaging lectures as this would be how it was asked on this new test.
This "new test" will probably not be graded as detailed as the thee digit scores we get for Step 1 and 2. It's been suggested it may become pass/fail to keep residencies from cherry picking based on Step 1 scores, but this guy suggested even the NBME recognizes their's value in having some degree of standardized comparison across different schools, so some degree of "grading" may be retained.
Of course it's being hashed out, so high shoolers now would be the only ones running into it.