However, what I really mean is, now that the Domain has come into play in a larger way with Halo 5 how would you guys feel about it being used as a facilitation for near-unlimited narrative flashbacks?

I could very easily see a spin-off series beginning, using the Domain in a way that's reflective of the Animus from Assassin's Creed. An ONI scientist starts investigating a terminal, and finds that he can relive historical moments that have been recorded in the Domain. This would allow the series to present similar themes and perspectives from various moments in the Halo timeline. I.E. the Human-Forerunner War, the Forerunner-Flood War, the San'Shyuum Schism, the Sangheili-San'Shyuum War, Etc... We'd finally get a chance to experience those historical battles from a first-person perspective.