For the record, I've never support microtransactions in any game. However, I feel like cosmetic microtransactions are almost essential in order to keep a game community alive. If you look at the first insurgency (No microtransactions, only client-sided customization) you'll see that there has been a steady decline in player base, even before Sandstorm was in view. PEOPLE WANT TO FEEL SPECIAL. The modding community can only get people so far. Because of this, I understand why microtransactions have been confirmed.
In list form, here are some idea that may help in the future:
Weapon camo. However, don't release ridiculous paint-jobs for our firearms.
Allow players to unlock basic, realistic camo like the styles already available. Make weapon camos very expensive, but rather than have one camo per firearm, allow players to unlock one camo for ALL of their firearms.
Voices. This one would actually be really cool and pretty unique.
Allow the player to unlock different voices for their character. You could record a pack of voices for one "season" and then work on the next pack during that time period. Get the actors from Generation Kill to do some voices (Ray Person, please).
Weapon Attachments. Don't make weapon attachments that already standard for weaponry unlockable.
Rather, allow players to purchase customizations for some of the attachments. I think the insurgents would benefit from this the most, while security would benefit from the camos most. I want a beer can silencer for my Uzi, please.
Things that will ruin this game.
Weapons. Do not make players buy or unlock weapons. This is absolutely imperative if Sandstorm ever wants to see competitive play. Allow the players to build their own meta around what's currently available.
Boosting. Don't include that little item in a game's shop that says "2x XP BOOST 1 HOUR - $3.99". With a game like Sandstorm, players will often find themselves struck by the realistic effects and audio. You don't need to make it about the grind.
Season Pass. I don't buy season passes because I know that developers aren't always trustworthy. Most season passes just barely make up for their costs with content. If you don't think you can release a lot of quality DLC for this game, then don't even try. It will just hurt the game's image.
Like, I said, I don't support microtransactions, but I think Sandstorm is different. It's such a good game, and I don't want it to fall off. Microtransactions should focus on making the game more fun without affecting the game balance. I hope NWI and FHI take this into consideration when they push for release.