Take FFXI as a game model:
its mechanics - its combat, its classes, its levels, its stats, its crafting - everything that is involved in the actual gameplay...
And just transplant it into an entirely new world in terms of lore, story, geography (along with updated graphics)

Wouldn't be so bad at all in my opinion
Would certainly have been a good starting point at least, better than simply throwing away almost everything, regardless of whether it worked or not.