Didn't laugh so much for a long time.
RMT is a market on its own.
If SE would bring in a bank with a moneylending system it could reduce RMTs a lot.
Lend X Gil by an NPC and lower all of your Gil income from drops, sells, etc. for a fixed percentage to payback the Gil. Fix the summed up reduction to a max percentage of like 50% and all would be happy, except gil sellers.