These are just some ideas that I thought of, not anything official.
Season name: The Beginnings
This would contain the Mark V core and Orion core, Cortana AI, 343 Guilty Spark AI, among other Halo: Combat Evolved related cosmetics and the rest of the Halo: Reach cosmetics. It would Contain some game modes including the Race game mode, and Anniversary slayer. Some weapons it would bring is M6D magnum, Classic Sentinel beam, and Okarda’phaa-pattern plasma rifle. It would also have a few new maps, including Chiron TL-34, Blood Gulch, Boarding Action, and Rat Race. Some vehicles would be Karo’etba-pattern Ghost, Oghal-pattern Banshee, M12 Warthog. The Fracture event would be ONI, It would have an ODST core and other ONI related content.
Season name: The Great Journey
This would contain the Mark VI core, Mendicant Bias AI, 2401 Penitent Tangent, Gravemind AI, playable elites, among other Halo 2 and Halo 3 related cosmetics. It would Contain some game modes including the Infection game mode, Grifball, Juggernaut, and Assault. Some weapons it would include is the M45 Shotgun, Sulok-pattern beam rifle, M6/R Spartan Laser, Type-25 Brute Shot, and the Type-25 Spiker. It would also have a few new maps Longshore, Heretic, The Pit, Valhalla, Terminal, Turf, and Gemini. Some equipment would be the Z-4190 bubble shield, Portable gravity lift, and Deployable cover. Some vehicles would be the Specture, and Barukaza Workshop Chopper. The Fracture event would be Blackguard, It would have the Blackguard core and many armors related to the Medieval time period.
**Season name: Reclaimer **
This would contain the Mark VI (Mod) armor core, Roland AI, 031 Exuberant Witness AI, among other Halo 4 and Halo 5 cosmetics. It would include some game modes including the Extraction game mode, Super Fiesta, and Flood. Some weapons it would include is the Z-180 Scattershot, Z-250 lightrifle, Z-390 incineration cannon, and Z-750 binary rifle. It would also have a few new maps Impact, Daybreak, Harvest. Some equipment would be the Regeneration feild, hologram, and autosentry. Some vehicles would be the Phaeton, and Ogab’d-pattern anti-aircraft Wraith. The Fracture event would be Forerunner, It would have the Prefect core and many armors related to the Forerunners.