The current ride is already described as “a colorful Southern bayou” by Disney:
Of all the objections that people have expressed about the retheme, the one about clashing with Frontierland makes the least sense to me given that the land is already geographically discordant.
Space/geography is one aspect of a theme, what it evokes is another. The time period of princess and the frog is so far gone from the Frontier. It is actually closer to the present than Main Street USA. Mix the time and space both being off, you do not evoke the themes the way Frontierland current line up and it's content does. It may not make sense to you, but it has points to most.