A nice feature would be to add a personal "bubble index", based on how much time users spend reading articles from "the other side". Some warning, "hey you live in a bubble, try reading this even if you disagree".

Also it would be nice to be able to rank articles by "least partisan".

Granted, I think the market for true nonpartisanship is pretty small. Kinda like health foods, where basically you just repackage sugary stuff with pictures of mountains on the box; with news you just have to convince the public that your extremely partisan corp is the balanced one.