Last night I looked up other members of the Dovyalis genus. If I were to experiment with graft compatibility, I’d first try Dovyalis rhamnoides, aka Sourberry. But I don’t know why anyone with a mature Kei Apple plant would bother with this because typically they are drowning in seedlings.
First ripe fruit of the season
Mine are finally putting out some new growth, lined with their needle spines. I think they like these 100° days and 80° evenings. They don’t seem to react at all to more/less watering, I think they’re pretty darn tolerant of both.