There are a total of ~230 NS spots in the country (ACGME and AOA). That's 230 out of some 26000 US medical grads and another 12000 foreign grads. Now sure virtually all don't want to do NS, but we're really talking about a residency that goes to people who either have connections or are at the very top of their classes (MD or DO). Please know that if this is really what you want you are going to need some amazing combination of constant very hard work (almost everyone works hard in medical school as it is) and luck. And be sure to start working on your CV from the beginning.
Last year 3 DOs matched into ACGME NS spots. It's clear that it is "easier" for an MD to match NS than a DO, and given the uncertainty associated with the merger, AOA NS residencies may not be a safe bet when you are applying for residency. That said, we are still talking about a residency that has very few spots and is virtually impossible to get for the vast majority of MDs, let alone DOs.
Bottom line: if you get into an MD school, go there and work your butt off because it'll be an uphill battle. If not, you're chances are better as a DO than any other options (close to impossible as a US IMG, impossible if you don't go to any medical school).