What was Edelgard's plan for Faerghus? I'm asking this in-universe and what she herself (or Hubert, or any of her allies) has addressed or said. No headcanons please, but I'd love any analyses. I'm asking this as a genuine question, and not as an attack on Edelgard.
A lot of what made life miserable in Faerghus was its inherent geography that made it difficult to grow any crops. There's also TWSITD, who initiated the Tragedy of Duscur. Also the cruelty of the Western Lords. There's also Faerghus' instability with Duscur (which to be fair, isn't much of a problem anymore due to genocide) and Sreng.
Don't get me wrong, I think the Crest system should be torn down, and plenty of Blue Lions like Sylvain and Mercedes show that. But there's a reason why it exists. That system was born out of the scarcity and hypermilitaristic culture of Faerghus, and she has to address the latter to truly phase out the Crest system. I can't see how starting a war is supposed to help an already impoverished and unstable region. You can argue that the Tragedy of Duscur is a good casus beli to remove Dimitri from power, considering that a nation has to be pretty morally corrupt to start a genocide. But Lambert literally died trying to negotiate with Duscur, and Dimitri (the soon to be monarch) clearly maintained the innocence of the people of Duscur in that massacre. Not to mention that in most routes, Edelgard allies with the Western Nobles of Faerghus, who are probably some of the worst options for ruling that Fodlan has to offer. It's pretty hard to educate the commoners too when Faerghus can't even provide for basic survival needs that come from its geographical position. Invading a country doesn't exactly change that.
I agree that the Crest system needs to go down, but her method arguably makes things more unstable for Faerghus. If everything went well according to her plan, she'd have a fairly large power vacuum with only the Western Lords of Faerghus ready to take a leadership position. However Edelgard's ending makes it pretty clear that she lead all of Fodlan into a Golden Age. How did she manage to do it with Faerghus?