If anyone is still feeling afraid that Shantae isn't "big enough" to be playable in Smash... you have to consider that characters have been added for many reasons beyond star power, sales numbers and fan demand. It mainly comes down to the whims of Sakurai, and at least for this game we know his team had some say in what got in, namely spirits.
Even considering they're owned by Nintendo, characters like Ice Climbers would be something anyone would reasonably expect if they hadn't been included until now. Sometimes they're franchises or games that Sakurai personally likes, like Mother, Persona 5 or Xenoblade 2. One time a third party got in because his creator asked nicely. Or they're included more for their historical significance than being popular, like R.O.B. Or most recently, flat out reserving a spot for a character in a certain series in the hopes of finding something good (Incineroar from Pokemon). Who is to say Sakurai won't want to do something similar for indies? Even if Shantae isn't the one he selects, it would still be very significant for those in general.