The way equipment works in the game, there has to be something compelling to make new gear since it's generally intended to consist of sidegrades rather than constant upgrades, and 'the same thing but with different flavor text' is unlikely to be something the devs are interested in doing. Also, given that the Champ is an outsider to Old Country culture and rectifying this is
outside the scope of the game, there's no real reason to think that because you're Keros' Champion you suddenly have the knowledge of how to properly conduct relevant Kerosite services.
Now, thematic gear
can happen (like you can get kunoichi garb) but unless one of the main writers
really feels strongly about it, the odds of miko garb getting into the game are pretty slim. Based on
some previous comments, user-submitted thematic gear could get implemented provided that the gear is appropriately balanced and (more importantly) contains a quest/dungeon in which you'd obtain the gear.