The trouble there is that they actually deliver on the immortality they promised. If you want to eradicate a race, why make them immortal? There is the possibility that it was all they had, but still, it is so ham-handed you have to wonder why even bother?
What I like about my theory is that it fits the Inchoroi MO of subversion over murder. Well, Aurang's MO. It is just as plausible that the Womb-Plague was just a Tekne bumble, but I don't much like the bumbling Inchoroi/Consult idea, even if that's how they often seem. They had a nearly impossible task and are doing what they can.
The Inchoroi probably figured that Nonman society couldn't handle immortality, since they knew how poorly thier own did. That's why they had no qualms about extending their lives for them, they knew it was a disastrous gift.