Here’s an idea…
If 343 are gonna add Halo REACH to Halo MCC, then they should also add a feature in that same update which allows players to wipe their campaign progress. This could be with 1 or all 6 campaigns.
A reset wouldn’t remove any rewards (nameplates, avatars, etc?) or achievements earned via the campaign, but it just means you’ll have to play the campaigns from the beginning, not being able to select a mission to play at any random time!
Overall… A button that gives us a clean slate to play the story of Reach, all the way through to the story of 4!
When Reach comes to MCC you’ll be starting with a clean slate for that campaign, as no 360 stats transfer over. No other Halo game has offered a way to reset stats so I don’t see MCC adding something like this in.