I think Step 2 and clinical experience will still impact. Downstate students seem to pretty consistently match at residencies at NYU, NYP Columbia, Cornell, UC schools, etc. going back into the 1990s from downstate’s website documenting residency placements. I doubt that step 1 being P/F will make that large of a difference for most students.
That said, very competitive residencies may be more difficult to get into, especially those that placed an emphasis on step 1 scores before. That might shift to step 2 or onto more qualitative measures such as research, extracurriculars, and letters of rec from the right people. It’s probably still up in the air until we get through a few cycles of students taking step 1 P/F before we can really be sure about what the impact could be.