I just had a dream last night, in which in one of the event's upcoming chapters, Sita appeared as one of the trials summoned by Indra, specifically to challenge Rama, and would stick around until the end of the event. She even had a special NPC sprite in battle, like Naucrate or Galahad, implying that she might not become playable right now, but she will be in the near future. Maybe they might release a bunch of new SR Servants for the anniversary right alongside two new SSR's. she might be part of that batch alongside 4* Rider slim Caesar, who was also in my dream, who knows?
All I know is that it was too good to be true.

Reunite them already, Lasengle you cowards