People may or may not already be familiar with Age of Empires Online, an attempt to revitalise the franchise that was lost when Ensemble Studios closed its doors. Like its predecessors, however, it suffers from forcing people to purchase expansions, whilst TSO provides the whole game to users through a learning experience, and offers Gems through both playing and microtransactions.
With so many other great ideas to make the game better - seasons and weather, nighttime, improvements to the interface, expansions to the water, etc - would it really be that hard to make The Settlers Online a proper MMORTS, but Free-2-Play where the microtransactions help fund its development? That way the game's universe would still expand, except the only money people would pay to expand their gameplay experience is gems, which they would be free to use on the resources/upgrades already present in the Trader area. It wouldn't be mandatory to purchase gems either; they could still collect them as normal, but all the people who purchased a certain amount could be flagged ingame and on the forums as Contributors towards its development pipeline.
This would depend on community support and the studios desire to make the full transition, but it's still worth consideration.