As a Shikigami, continuously and efficiently supplementing the power of "spirit" from various sources, should eventually enable one to become a deity smoothly upon finding a suitable Divine Remains Bone in the future.
Lastly, there's little Satoru.
Satoru is quite special; her qualifications to become a deity are much weaker, and she's basically an appendage for collecting the "Seven Sentiments Oath."
Moreover, possessing the "Future Sight," she's inherently not adept at battlefield combat.
The strategic significance far outweighs the practical significance of being on the battlefield.
Of course, Kamiyagawa will still strive to cultivate the sister-in-law into a deity.
After all, the "Future Sight" is really useful.
