Two come to mind.
The first being: a 'Cosmetic Weapon' slot.
As a character that uses a sniper rifle, an assault cannon, or even a regular rifle, you can look pretty bloody dope. You can have on the best armor, the shiniest weapons, the coolest cosmetics, and when it gets down to executing someone, you...
Pull out an old, bog-standard piece of **** blaster pistol and shoot them.
Um, excuse me, I have a rifle with a freaking laser sight on it!
A cosmetic slot would be very, very nice to just let us use some other pistol than that piece of **** default thing we're forced to use. It's not a huge deal, but it would be nice!
The second one: Voice modules.
I love the modified voice on certain masks. It sounds ridiculously awesome.
You also can't get it unless you're level 40+ and a tank. Level 50+ if you're light/medium armor. Or level 1 if you have a cartel market cybernetic upgrade and want to look absolutely hideous. None of those options are ideal. Not in the least because by the time you get the damn helmet, you've done everything already.
So, add a 'voice modulator' slot to any closed-face helmet. Put up a pack for 200 cartel coins that had voice modulators in it. Rake in the money.
Alternatively, add in the ability for artificer to create voice modulators to replace the crystal trade that the Cartel Store absolutely murdered.