Speaking about barter. Warframe already do that. However the community built a website called warframe market, which is basically a hub for seller to adv their items. The transaction is done face to face between seller and buyer, which kinda makes it more intimate compared to buying straight from MB.

However it is time consuming, because seller and buyer need to be at the same place to make a transaction. Its not rare to get a PM from buyer when you are in the middle of a mission and when you done, the buyer already bought it from someone else.

Although for me the real answer to this problem is by introducing socialism and progressive tax. Or.. maybe just forbid/limiting gil transfer between players.