Different from the alt versions of characters in Fire Emblem Heroes, the resplendent versions are designed to be alternate artwork for their base forms, and feature the character in clothing from one of the kingdoms that feature in the apps storyline, such as Nifl and Askr.
I designed the Corrins wearing clothing from the realms of dreams and nightmares, as it fit the split nature of Nohr and Hoshido in the original game of Fire Emblem Fates.
Only time will tell us what their actual resplendents will be, and if they will get one.
The female version of Corrin dressed as a Ljósálfr, with colours and design elements taken from the Hoshido Noble class.
The male version of Corrin dressed as a Dökkálfr, with colours and design elements taken from the Nohr Noble class.