My idea is a Decade down the line when the plague has passed and Corvo is now just the protector of Emily. The outsider becomes bored of Corvo and demands the powers he gave Corvo back, but he refuses and the outsider becomes furious and decides to make Corvo's life a living hell and make things interesting by starting up a rebellion with the poor people of Dunwall and giving a select few who have had their lives ruined by the government and the guards, similar powers to Corvo's. Most of the Survivors of the plague are a lot poorer than before the plague and are already unhappy in the squalor that they still live in and the outsider invokes anger and chaos into their minds with magic to make them rebel violently. The only way for Corvo stop the outsider from winning is to destroy shrines dedicated to the outsider which belong to a cult worshiping the outsider and have now got rebels protecting the shrines.
My ideas a bit short and not fleshed out but I think it could lead to some interesting gameplay as you could play as Corvo and the people who were new to the powers. This could also lead to a lot more interesting characters that play roles in both sides of the rebellion.
I'm interested in what other peoples ideas are I tried to make it suit a game like Dishonored and have an interesting story it may not be perfectly in line with every bit of lore though.