From June 2019's MCC Development Update:
Quote:When a season ends, nothing will be taken away in terms of unlocks. If a new season starts that has a new theme, such as the release of the next title for MCC PC, it will be additive and include new unlocks to work towards. For you, this means that if you haven’t finished unlocking all content for the first Halo: Reach season, and the Halo: Combat Evolved season has started, you now can choose to continue working on unlocking content in the Halo: Reach season or use your season points towards the unlocks from the new Halo: CE season.
So it seems that when additional titles are added to MCC on PC, the new Seasons will reflect content for these games. That said, I am not sure why kind of content could be added for the other Halo titles besides Nameplates, as there is not armor in Halo: CE and we have everything unlocked in the other Halo games. Perhaps they will re-lock the Armor?
However from that same Development Update...
Quote:In future seasons, we are looking into ways to expand the pool of customization items in each game. At minimum we would like to include new profile items such as nameplates, but we think it would be even cooler if we could add new skins, armor or visor colors, or armors to the other games.
I have seen how Halo 3 can be customized to include things such as visor colors or even light colors. Perhaps this is what they are referring to. The idea of new armor added to Halo 2 really excites me, but perhaps it will just be added to Halo 2: Anniversary. Only time will tell!