In past games, getting armor ranged from very easy, to very hard. It usually involved achievements, Campaign missions, and Multiplayer. Halo: Reach changed this up a little. Basically how it worked was that it used a system called Credits, or cR. The way to earn credits was to play the game. You would earn credits for Forge, Customs, Matchmaking, Campaign, Challenges, Commendations, all this. No doubt will Halo: 4 have more armor options, however how will we unlock and use this armor? How about a combination of both systems?
You start the game for the first time and you have the default armor, whether it be Mark V, Mark VI, or Mark VII. The way you would unlock armor would be to complete challenges. These challenges would stick for a very very long time, and they would be very basic, yet some would be difficult. Perhaps there is a mission in the campaign where John gets Mark VII armor. The starting armor for Multiplayer is Mark VI. One of the challenges could be complete that mission, and you get full Mark VII armor for use in the Multiplayer.
Example: One of the challenges is to get 10 Sniper Kills. This would unlock, say the shoulder pads for Scout Armor. Get 100 Kills and you get the Chest Piece for Scout. 200 Sniper Headshots and you earn the Helmet. (THese are just random numbers, you could need many, many more kills than this in the final game)
Recon Armor (Being a Stealth based armor) would require objective scores like Flags or Bombs. 1 Flag/Bomb and you get the Knee Pads, then say 500 and you get the full armor set.
This could play into the Multiplayer lobby. How? Well many people like to judge people based on rank, their Service Record, all this stuff. Say you see someone with full Recon armor, you would know to make sure they don’t get near the flag because to earn that armor you will need a lot of objective based kills. This could bring back that feeling that you had for wearing armor in Halo: 3. It meant something. It was difficult task getting certain armors, so wearing them gave you the feeling of accomplishment. With this armor system, you could get that same feeling of pride for wearing you armor, knowing you had to work really hard getting that armor.