Honestly, I would take Quote or Curly Brace from Cave Story any day before Shovel Knight. I liked the game a lot, but he seems a bit plain, imho. The odds of any of them getting in, however, is pretty slim. I agree with that argument that SK isn't in line with Sakurai's definition of iconic...
That said, I'm not going to be too choosy with what characters get in. Just because I'm not a huge fan of Pac Man as a character doesn't mean I feel he shouldn't be in the game. Any character that gets in, gets in, end of story. You can play them if you like, I just won't.