Having free trade as members' benefit could be a an incentive to players to upgrade to members, as well as the more enjoyable gameplay will encourage them to stay around longer. However, this would not be a popular choice for OSRS gold free players as it would mean that the wilderness could be removed again. Freeplay might allow the return of PvP to these areas, giving those who prefer it to Wildy a place to PK in the wilderness.
Jagex's integrity is what I think would suffer the most. Although this would be a great step in making the game more enjoyable however, some players might see that as a sign of indecisiveness and flimsily attempting to bring the wilderness back. It is an unwise business decision to allow players who are unhappy and quit to make as much money, which would likely increase the number of players in the long-term.
Although this won't solve all of the freeplayer's botting problems (as as it doesn't do anything for members), I think it's reached the point where a significant step such as this will be needed to stop the RWTers and bring freeplay back to cheap RS gold the game that I knew. Jagex must intensify their efforts in combating bots and bot makers, as well as make visible progress and provide public updates.