I'll give an opinion from a non Nintendo fan. Pretty much what is always mentioned. Ninteindo fans love most Nintendo games regardless of genre and/or quality, and most official Nintendo character that they don't know of get immediate praise from them. Nintendo notices these characters are popular and strikes while the iron is hot. So these characters get a brand new game(sometimes even after the series being dead for over 20 years,) get a major part in a future game in their series, or get brought back for several games in the series whether it's an appearance or as a main character.
Just watch. Rosalina is going to either get her own game or have a significant role in future games.
*edit*
I just thought of this. Nintendo fans rarely ever get brand new IPs, just new characters who work their way into pre existing IPs. Nintendo fans have to hype up atleast something new.
