But I think that he probably never really held back when working on medical problems. He would never have been OK with people dying just so that he could keep his genetic enhancements secret.
I agree with this. I also think that's why he became a doctor. He said his parents had a good doctor do his genetic engineering, but others weren't so lucky. That makes me think of the "rejects" in Statistical Probabilities. He knew that could have easily been him, and he wanted to be the doctor that saved people. It would have been interesting to see him do some intergalactic "doctors without borders" work, where every person/being he saved was one less person that could be harmed by a hack. That would have been good. I honestly only see his revelation as a good thing for the character.
I read somewhere once that Siddig said that he didn't like that twist in his storyline. I wonder why? It really helped his character, at least to me it did. The section 31 stuff was just great. Sisko actually had him being a spy with that one. No holosuite required.