[TheRaizin]

Said it once and I'll say it again, Reika Shindai has the most likelihood of becoming a Kamen Rider, with Luna being a close second.

Not only does she slightly resemble the female Zweihander-holding swordswoman in the teaser trailer, she has "Shin" in the name of which means "God"; many characters that have anything resembling either "Kami" or "Shin" in their name are also riders. Sora Ogami being the exception since he's a kid. She is also being set up as a threat to Touma, much like how Gai was to Aruto, except the Kamen Riding part still being unknown if she is or isn't.

If we are to believe, that the smoke that took Kurayami and Sophia is her, it's clear she has some power sets as well (Smoke-themed rider?). I'd say she has a good chance of being either a Kamen Rider or a kaijin.

As for Luna, we haven't seen what she looks like currently. She'd obviously be a lot older now. Since SOL has no knowledge of her outside of Kento, she could be out there trying to survive in the wonderworld. Hopefully as a Kamen Rider.

However, it could be that Reika is also aware of Luna and has her imprisoned somewhere, making her the classic "damsel-in-distress" character for Touma to save. Not a fan of this speculation.

Edit: the woman was holding a Zweihander. Kurayami was the Flamberge.