The first ever mention of Kainestones is in the lore story "Insights"

"Kainestone was a powerful resource used to fertilize land due to
its magical properties. She read on to discover that research was being
conducted to find out how else the stone could be used."

The second reference is in the lore story "Understanding":

"What is important about the kainestone?”
“It’s a recent discovery in this region, the Red Hills. The people here
have begun to mine it. It is rich in mana and makes the land fertile.
The Xenith Scale, however, fears it can be used for a different purpose
in the hands of the Chaos Legion. Perhaps as an agent to make their
spellcasting more powerful.”

The next reference is in the lore story "Defenders":

“What demands has Obsidian made?” Bera inquired. “Our complete and total surrender, our kainestone mine, and all
research assets involving kainestone. I truly do not know what she
wishes it for. It has amplification properties of earth and fire mana.We
use it to enhance our farmlands.”

So it's mentioned in at least 3 lore stories so I believe that we will be able to farm this resource in the land expansion.