An illithid plot, a githyanki companion? And no githzerai in the mix? Unacceptable!
In seriousness, I wouldn't worry about githyanki being a separate race. That could be for engine/reactivity/tagging reasons. Or as to keep the secret of playable githzerai from the players. However, what makes me worry we might not see githzerai is that while they're one of the best races for the game narratively, they're also one of the most difficult to implement in terms of reactivity. They are a very alien culture, which would need custom interactions, like githyanki; but they're also very different from githyanki culturally, so their dialogue couldn't be copy-pasted.
I really hope they're added though. Such a great fit for the game; would be a wasted opportunity.