So the current plan is to shoot for AOA ortho (and maybe use gen surgery as a back-up for AOA, undecided on that right now). If I didn't match there, I would still be able to go through the ACGME and shoot for something like PM&R, EM, or family med (and follow through with a sports med fellowship) which I should definitely be able to get assuming I don't completely blow boards and third year. I'm actually hoping that the merger will not have occurred by the time I match so I can use my above plan. If the merger happens then I'll have to figure out if I'll have a legitimate shot at ortho or if I should pursue something else. This will be very, very dependent on how my boards turn out.
As for the PD after the merger thing, I think it depends on the field and program. I believe ortho doesn't get many ACGME matches for a few reasons. The first is that it's extremely competitive, so not applying AOA is a huge risk for any DO. If you match AOA ortho, you are then automatically pulled from ACGME. Since the better applicants will match AOA, I think most of the less favorable applicants forgo ortho in the ACGME match and shoot for something else (as I probably would). If they did decide to go for ortho, they'd be up against a group of MDs who typically have very strong applications, usually better than theirs. Combine that with the DO bias that I'm sure exists at least at some programs, and you get the results of very few DOs going into MD ortho programs (which is what we see). After the merger, no PD will be able to explicitly say "No DO applicants allowed". I do think you are correct in the sense that the attitude about not taking a DO will likely continue at many programs, especially in highly competitive fields or some top tier programs. However, I'm guessing you'll also see many former AOA programs continue to favor DO students over MDs to offset this, but that could be wishful thinking on my part.
That being said, a DO is still capable of entering any field and can get into an ACGME residency in any field (even if some specific programs hold a ridiculous bias). Some fields, like plastics, it is incredibly difficult, but it's still possible and more dependent on the individual than anything else (just like anything in medicine).
Idk, I think you should be fine for your field. Over the past 2 years the vast majority of our 20ish people to go psych went ACGME (16-17) and 3 or 4 of them ended up in the NE. One of them even went to Harvard South Shore (can't remember if that's one of the 3 solid ones in their system or if it's one of the meh ones). MD will almost always give the edge at ACGME programs, but I would think you'll still be fine at most places for your desired field. If you don't mind me asking, any particular reason you want to stay in the state you're going to school in?