I wouldn't say "most". She was mentioned a fair lot in leaks. It was only a matter of "When?"
I think Richter so far is the most unexpected, people weren't sure we'd get even one Belmont! Still, she seems to be very unexpected among people who don't follow leaks (or Smash info in general)
The most unexpected addition to Smash Bros. by far, but I welcome it.
I'd say she's only unexpected, if you didn't expect another Animal Crossing character in the first place. By now, she's pretty much the most popular AC character. Also, she's an Assist Trophy in SSB4, so that's practically a promotion.
