Full Credit/Trade system/Auction system.
This is something i feel could be easily implemented if coded correctly. A full on Market style system. Keeping the traditional Cash Shop concept but expanding onto it with full featured menus and such. Something like a Live Auction system accessible through an NPC in BI that will allow players to auction items for credits or whatever else. This could help newer players (like myself) to earn some credits a bit faster. Especially if all you have to offer currently are small 1-5c frags and such. This could really revive the economy and also help put some player controlled price checks/balances into place.
We've been fighting to have this for years :(