All those at top 25 (maybe even up to top 40) ranked MDs will want this change. All those at low-tier MDs and DOs who are interested in primary care/non-competitive specialties or do not particularly care to train at a top residency program will want this change.
People who want to restructure medical education to have less wasted time in the classroom (especially when many students forget everything and have to relearn everything from Dr. Sattar, Dr. Ryan, and UWorld) and more time for clinical education will want this change.
People who complain about the nebulous COMLEX average changes year by year, well there's a decent chance now that Level One can become P/F, so that will be a welcomed change too.
People who complain about lack of quality/stratification in some DO schools - well now is the chance for certain DO schools to improve themselves and advertise they provide a superior product by having strong clinical training, research opportunities, and extensive GMEs. Hopefully, there'll be an official DO school ranking list soon.
----------------------------
However, those of us who are/will break(ing) barriers by matching in excellent residency programs - this is a shame. Imagine coming from a background where you can't get into a top undergrad that feeds into strong medical schools. Imagine making some stupid decisions (so many of us do) when you were in your late teens/early twenties such that you're no longer able to go to a higher ranked MD later down the road. Imagine being from Cali or a state loaded with premeds so you have to apply out-of-state and have to go a low-tier MD or DO despite having good overall matriculation stats. Step 1 was supposed to be a great equalizer there, now it falls to Step 2, but the timing of that exam hurts a lot of people.
Many will benefit from this change, but it utterly screws a significant minority of excellent medical students.