when it comes down to it, and to get back on topic, a huge reason RMT exists behind the scenes in osi UO is specifically because of the sub fees. many players just want to keep there accounts open. providing an easy gold source for the more prevalent third party sites. leading to more gold being more easily available, which contributes to in-game inflation.
I cant see UO ever fully embracing RMT, such as in other games, most notable one "Entropia" that actually encourages and is based around rmt sales of virtual items / properties by design. i think this game still holds the record for largest virtual property sale ever, planet Calypso, for $6million.
what i can see being realistic is a system similar to world of warcraft, that now allows players to buy game time tokens from blizzard, and then sell them on the auctionhouse (for an amount partially fixed by blizzard). this allows players to basically "buy gold" from other players in exchange for gametime.
I can see broadsword doing something like this. a very basic system that would solve both ends of a problem, some players need for gold, and other players need for gametime.