The trend that's partly coming from the Spirits trailer is more the Possession deal rather than the outfits. Basically, after someone mentioned the idea that the fake characters are possessed by the Spirit, someone made artwork of Samus being possessed by Shantae, because of this image, hence the whole Samus-Shantae deal.
However, the other thing that got the Possession deal going alongside the first Samus-Shantae artworks was from none other than Aykk92, A.K.A. the creator of the original Bowsette comic, which showed various characters possessed by different characters, like Wario possessed by Ouendan and Mario possessed by Sephiroth.
While the trend hasn't spread to the popularity of Bowsette(even with Aykk92's comic), it has been slowly growing. Shantae-Samus is still going strong and the reason Pyra-Lucina exists was that someone asked if someone could do the same to Lucina who was possessed by Pyra in her Spirit showing and someone did. And by what I've seen, that one is also slowly growing compared to other possessions, but not as much compared to Samus-Shantae.
But the possession deal itself is slowly growing, as there's artwork of various characters possessed, like Cia possessing Zelda, Liquid Snake and Ocelot possessing Duck Hunt, Female Corrin possessed by Sakura, Olimar possessed by Camilla,
SNAKE possessed by
ELISE, an Octoling possessing an Inkling, etc.
