For instance, lets say Trump creates an executive order demanding that a wall between Mexico and the US be built by 2018. Both the right, and the left, will write thousands upon thousands of articles about how this will be great for the country, and terrible for the country. The truth like most things, may lie somewhere in between the extremes. Your news aggregator would allow you to read articles about the wall, as written by both conservatives, and liberals.
Then, you'd at LEAST be reading the differing opinions. The problem is, I doubt many people would want a service like this. Like it or not, human beings seem to enjoy the comfort of their solidified beliefs. It's far easier to digest your right wing, or left wing news, rather than digesting BOTH. People don't really want to change.