I think Sakurai could possibly make Reimu work for the West depending on how she is shown. With Hero, aside from Dragon Quest's popularity in the West, the other thing that sorta got people not caring was the fact that Hero is a sword character. With Terry, while people didn't know who he was and compared him to Ken, once people saw how he played in Sakurai's demonstration after his initial reveal, a good number of people's stance changed on him and people began to lean toward him.
If Reimu were to be the 5th DLC character, they would need to sell people on design, moveset and who she is for people who don't know her.
-First the design:
When it comes to the design, Reimu is basically a shrine maiden. It sounds basic on paper. But that being said, she has a very distinct design that really helps differ her from the rest of the Smash cast. With Hero, people compared him to Goku and Link. With Terry, people compared him to Ken. Reimu has no one even remotely similar to her in Smash. This allows her to fit in into the Smash cast with her own unique look to her while not taking any uniqueness away from the rest of the cast.
-Second, her gameplay. This I feel is what can really help her case in winning those who don't know her. She is a shrine maiden from a Shoot-em up series focused on dodging a ton of enemy bullets. Just from the concept alone means you have alot of chance to surprise people with her moveset, especially if they do go all ham and flash with her. Just the idea of people seeing her shrine maiden look, thinking of her as a kind of magic user, to suddenly seeing her firing her spell cards and magic like frickin' laser beams and whatnot. Inspiring her gameplay around the Shoot-em Up genre would not only give her lots of originality for those who like original movesets, but also win over people who love Shoot-em Ups.
-Third, who she is. After Sakurai's showings of Hero, Banjo and Terry, it wouldn't be surprising if Sakurai did the same for Fighter 5. Considering how Sakurai's showing of Terry and his knowledge of SNK helped people warm up to Terry, I'm sure he could do a very good showing of Reimu as well and get people up to date on who she is and her genre.
Basically, if all 3 are handled well, especially her gameplay, I'm sure Reimu would be able to win over people who don't know her or her series.