At the risk of epically noobifying this thread, why is Vehk is only one? (Attaining CHIM, that is) Ayem and Seht equally shared the ineffable sense of godhood, and were liberated from the laws of all divine worlds. Seht probably moreso than Vehk.
If godhood was just a step on the journey to CHIM, then CHIM wouldn't be as meaningful.
Someone has to be the guide. In some native American myths, it's the crow. Normally they're completely amoral, as they are beyond distinctions between good and evil. Crows are also carrion-eaters. Levi-Strauss wondered about this and came to the realisation that it's a reflection of the crow's liminal nature. As a guide, he has one foot in both worlds. As a carrion-eater, he is not only of the living and the dead, but he represents an intermediary between the plant and the animals eaters, the agricultural and the hunting realms.
In Ancient Greek myth, the guide is Hermes, who's also the god of messengers, commerce, thieves, travellers, journeys and literature. He's also a psychopomp. It's from his name we get the word hermeneutics, the act of interpreting hidden meaning. Syncretism combined him with two other Egyptian gods: Thoth god of literature and magicians, as Thoth-Hermes, who to quote Wikipedia "served as a mediating power, especially between good and evil, making sure neither had a decisive victory over the other" and "appeared as an ape, A'an, the god of equilibrium,"; and Anubis, god of death and embalmers as Hermanubis.
In Christian religion, the guide is Jesus, who acts as a bridge between heaven and earth, life and death, sin and redemption.
Noticing a theme? All of these figures are about overcoming dualities, or bridging gaps. Vivec, like the previous figures, is a bridge between opposites. Male and female, god and mortal, "good" and "evil", and, to a lesser extent, life and death. And it's his role, as Mephala's replacement, to be the revealer of hidden knowledge, and the guide between those worlds. And what's CHIM but a state of mediation between dualities?
Technically, he was since a god "always" exists.
But let my try to explain it better: Vehk (the mortal) wasn't a hermaphrodite; Vivec, that is, Vehk-and-Vehk (the god) is.
The old "Vehk" timeline, which doesn't exist anymore, had Vehk as a man...
Vehk the mortal and Vehk the god exist concurrently. Hence why he's twice Vehk, or Vehk and Vehk. The old timeline still exists, which is why he can http://www.imperial-library.info/mwbooks/battle_redmountain.shtml.
And, well, http://www.gamesas.com/bgsforums/index.php?s=&showtopic=600610&view=findpost&p=8750313!