What he's basically asking for, is to go back to the prior themed season and progress that season. Halo MCC has that system in place, as its Battle Passes are also free and themed to the season (Season 8 is historical, Season 7 is Elite-themed, etcetera)
However
The key difference that u/shy-but-hopeful isn't considering, is that Halo MCC's Season Points are earned exclusively from Challenges (and rank to 100). Scrip for this season is earned from events specific to this season (as well as the Pass Progression itself). GSG would need to not only work around the UI to present multiple seasons, but develop new methods of delivering Scrip beyond the ones for the specific season.
I'm no Dwarveloper, but those are the issues I can see from my armchair.
That’s pretty much the deal, yes.