Combat prestige or out of battle pass leveling would be the generic leveling system for infinite. This has literally infinite levels with you working towards them to get basic rewards with an unlock every 5-25 levels with rare items every 100 levels.
You would gain XP for this separate from the battle pass XP which is only gained by weekly challenges, though said challenges work towards both battle passes and Combat prestige levels.
Function of idea.
every level: you get a challenge swap
every 5 levels: you get an XP booster
Every 10 levels: you get 50 Halo Credits
Every 50 levels: you get a rank emblem (chest, vehicle, gun, and profile) these are your actual rank levels
With these every 100 levels has a unique reward, be it a spartan armor part, a weapon skin, or a weapon model.
100 level item examples
Level 100: Ma5B model swap for the Ma40
Level 200: BR85HB model swap for the BR75
level 300: Chief’s armor coating for MVII
level 400: swords of sanghellios sight model for BR75 and commando
level 500: Unique kill effect ashes to ashes (turns targets to dust.)
These are along with the things you get every few levels.
With this would come an XP system change,
the forula used would be score/10 rounded up to the nearest 10. meaning if you get 2375 score in a match you get 240 XP for that match.
Note this doesn’t stack with battle pass XP which would still be at a slower rate.
Now for the really fun part the Prestige part of the name This comes after 1,000 levels you can Prestige your rank this resets your level back down to 0 with you being able to climb back up the 1,000 levels again. to make this worth it, each set of 1,000 levels has a different 10 unlocks and a different set of rank stickers you can unlock.