I remember there being some discussion about Simon as a wanted addition back during Smash 4's heyday, since he's considered a classic third-party NES/SNES icon along with Mega Man, so I wasn't surprised at the leaks/reveal of him. I heard more about Simon than I did about Isaac or Skull Kid, which is why I was surprised that those latter two were so discussed last year, since I'd never heard them be hyped up before. But I didn't peruse the Smash community too closely until last year, so what do I know.
Richter was the real surprise. No one anticipated him. But from what I heard, it has to do with the fact that Richter is more popular in Japan than Simon is. Makes sense, given that Rondo of Blood was Japanese exclusive for many years, and was apparently very successful over there despite that.
Dark Samus, too. Chrom's been requested since forever, since he's apparently popular among Fire Emblem fans as the main character of Awakening, so he wasn't a surprise, but Metroid fans primarily only cared about Ridley. I never saw anyone really bring up Dark Samus, since she was only in two games and is much less popular and well-known than Ridley. The only time people started discussing her was when there was evidence for her based on the E3 demo, with the DS alt color for Samus missing, Echo Fighters being introduced, and the DS Assist Trophy not having been shown. Before that, hardly a soul considered her.
I'd love to see the raw ballot results and figure out how the hell Dark Samus came ahead of other potential Echo Fighters. Whether or not I ever understand that mystery, though, I'll be extremely thankful.