The Path is Yoshiro becoming an abode for the Goddess. In the Mikoshi post, I showed how the localization implies this.
The mountain is alike the Goddess's body, and so when Yoshiro acts as a substitute, she absorbs the defilement from the mountain into her own body and becomes defiled instead of the Goddess.
Sometimes I like to imagine the Path as an actual physical journey with only the Maiden and the Messenger. Very Ico-like, if you will.
The mikoshi could be smaller and Soh could have the ability to interact with the physical world, allowing her to pull the mikoshi. (Yes, I want to be the one to pull Yoshiro!!)
I wonder what kind of journey they would have? What trials would Yoshiro endure on such a Path?
For a sequel, it could be a re-imagining of Kunitsu-Gami, allowing them to explore more ideas with their original concept. (I believe Evil Dead did this with its sequel. A remake and a sequel.)
I don't see how a normal sequel is possible without ruining the original. Sometimes things are perfect alone. And when they're perfect as they are, a 'requel' is an option: same concept, different execution.
All I know is I'd love to play this kind of story but only with these two characters.
I think this game is very special and very mystical with the ideas it presents.