We've Seen This Before
The system's closest analog would probably be "Rainbow Six Vegas 2," which let players earn experience in single and multiplayer. Experience unlocked new customization options, but those customizations included new weapons, more durable armor, elements that actually impact gameplay. Bungie went the other way by making all of the unlocks purely cosmetic.
It's no different from "Halo 3." In "Halo 3" you unlocked armor by playing online matches and the campaign. It was more tied into your ranks and achievements, and you couldn't choose which armor you wanted to unlock when, but the end result was exactly the same as what they're proposing.
Not A Big Enough Carrot
And here's the problem with that: It's not enough. Unlocking a new rank, or a new piece of armor isn't enough to justify me playing for another hour, giving me that "Just one more match" feel I get with games like "Bad Company 2" and "Modern Warfare 2." There's the whole carrot-on-a-stick mentality in online games these days, and what Bungie is offering isn't a big enough carrot.
What Could've Been Done
What I'd like to see are more meaningful unlocks which work with your style of play. I'm gonna propose something that would change the foundation of "Halo" gameplay, but I think it's time: No more weapon spawn locations on the map. You should be able to spawn with the weapon you feel most comfortable with, or you think is best in the given situation. Instead, you have folks fighting over sniper rifles or having to use weapons they're unskilled at. Your starting weapon could be unlocked via credits, so if you're more of a close-range player you could focus just on shotguns and SMGs.
Take it a step further and you can look at unlockable armor which actually affects gameplay. Lightweight armor which increases run speed (or allows you to sprint, as seen in the trailer), heavy armor which is slower but more durable. Again, this is all about putting the control in the hands of players and letting them decide what style works best for them.
Better Luck Next Time
Now granted, this is a massive overhaul of the "Halo" franchise that simply won't happen in "Reach," but I think it's due. Players want to feel like the 6 hours they put into the game on Saturday has some impact on how they play on Sunday, and a visual armor upgrade (especially for a game that's almost entirely played from the first person) just isn't enough of a reward.
I realize what I'm inviting here: A large amount of hate from "Halo" fans who think I should just go and play "Modern Warfare 2." But I feel like there may be a group of you out there who feel like these sort of changes are due for the franchise, and that drastic shifts need to be made to keep "Halo" as addictive and entertaining as it once was. I also realize that there are elements of "Reach" that have yet to be revealed, and my issues may be mitigated by other features in the game.