I think the armour system could work like this: You need to unlock each armour piece, be it with credits (similar to Reach) or commendations (similar to Halo 4) and it should cost credits to buy the armour skin (again, similar to Halo Reach, except with skins instead of attachments), so it's basically combining the Reach credit system with the Halo 4 commendation and armour skin system.